What to upgrade Next

a 450 gts isn't really a powerful video card. i would start by swapping out your motherboard/cpu/ram to something more modern. or swap the video card out, cause thats gonna have to be done eventually anyway.

Definitely start by upgrading the RAM, you can only go up to 4GB since you are using Win 7 32Bit, so getting anything over 4GB would just be wasting your money. The GPU would be your next upgrade, what is your power supply?

But it depends, are you looking to completely overhaul your entire PC or just looking to get the best performance possible out of what you currently have to work with?

You are being held back by the 2GB of RAM for sure. 4GB is pretty much necessary for gaming and 8GB is really the sweet spot. The bad news is that you have old DDR2 that is hard to find and expensive these days. I would look for a 4GB kit of 2 x 2GB so it will run in dual channel as well and just scrap what you have now.

If you have aftermarket cooling or are willing to spend ~$30 on something like a Hyper 212 +/212 Evo you could probably get that Q6600 to 3.2-3.4Gz and that would help as well. You still are not going to max any newer games with that system but more RAM and overclocking the CPU would help.

You might just want to save money for a complete system overhaul. What you have is getting pretty out dated.

i wouldnt spend any money on a ddr2 kit. save what you would spend on that (as ddr3 is cheaper) and upgrade your whole platform.

I would advise updating the ram *only* if you can find it cheaply...

The biggest upgrade I ever made for my PC was a SSD, its amazing the difference it has between load times in BF3... defo go down that route.

I believe Toms has done some previous posts of this sort of answer before, and an SSD came out on top.

Ash

an ssd is not going to help his frame drops.

Nope. Not at all.

when you swap motherboard cpu and ram you would be best off reloading windows. whats your budget?

A new motherboad will require a new CPU (yours wo n't fit) and DDR3 memory (again, yours wo n't fit).
The games you're playing are quite dependant on CPU performance so pushing it harder will be a big help, grab a half decent cooler and give it a good overclocking.
At that sort of resolution the graphics card takes a real hammering, especially if you push the eye-candy so a GTX660 or HD7850 should improve matters no end.
Add another 2Gb module so the system can run dual channel. Try to match the one installed, but do n't worry too much if that's not possible current systems will allow 'pick and mix' memory without too many problems.
As has been said, a SSD will not help framerates.

If you can, match the module already installed, at least for speed and timings if not maker. Do n't worry if you can only find a faster rated module, the motherboard should run it at the speed of the other unit, you'll loose a TINY, TINY amount of performance, do n't fret over it.
Overclocking can be frought with dangers, and like anything dangerous should be approached calmly and with plenty of research beforehand. Why not start by taking a look at the overclocking forum here?
Some coolers are that simple to install, most, sadly are not. Take the side panels off the system and look at the back of motherboard tray, a lot are a solid steel pressing but if there's a large square or rectangular hole in this pressing that exposes the underside of the motherboard and the CPU mountings things will be much easier and the choice of coolers wider.
The GTX660 tends to be cool and quiet, even with a stock cooler (fan at one end, blows hot air through a grille in the backplate) the HD can be a litte noiser.
If you don't want to use high levals of AA you can save a little by opting for the GTX650Ti or 1Gb version of the HD7850.
Me, I'd drop a 1Gb HD7850 in and be done-but then again, I'm lazy !

Upgrading your GPU will give you the biggest boost in your everyday gaming, much more than a CPU upgrade (a CPU upgrade will basically require a complete system rebuild and a fresh install of Windows). For £150 or about $230 US you can get a very decent GPU. I would go with a Radeon 7850, it will be a major upgrade as far as gaming goes and I would not consider it way too overpowered for your current system. Just make sure it will fit in your case and your power supply can support it. You say your PSU is rated at 520W, which is basically at the low end of the recommendation. That would be my main concern.

yes a 7850 would be a good upgrade alongwith another 2gb of ram and a good psu. honestly though you should go for a full system upgrade if you can spare the cash.

More memory will not help, a 32 bit OS can only use a total of 4Gb this might help explain:

http://www.techpowerup.com/forums/showthread.php?t=91260

A HD7850 would be the very, very top card I'd think of installing, even if the Q6600 was overclocked, without an overclock the 7790 is top card with the GTX650Ti coming next while the HD7770 is something of an also ran, a better card than the existing GTS450 but not really enough of a jump t really justify the expense.:

http://www.tomshardware.co.uk/gaming-graphics-card-review,review-32654-7.html

They're only two tiers apart.
The i3 is a fine gaming CPU and can give more expensive quads a run for their money but you'll need to add a new motherboard and memory to make that upgrade happen.
I'll suggest you drop a HD7790 or GTX650 in there, enjoy your gaming and start saving up for a whole new rig.
Or you can buy parts in order: Case>HDD>optical drive>PSU>OS>CPU/MB/RAM>Graphics card>Everything else.

First off you need to move to a 64bit OS. 32 bit operating systems can only address a maximum of 4GB of system ram, this included your VRAM. Moving to a better video card at this point, presumably one with more memory, will land you right back where you started, with only 2GB of addressable VRAM.

Second, If you're considering a motherboard change then it's time to retire the system and build a new one. There is no sense switching out motherboards if you're going to continue using antiquated tech. Plus it's a lot of work to go through considering there isn't much to be gained by it.

Moving to a modern intel i5 processor or even an AMD FX processor would be highly recommended. Take a look at cpu scaling in Crysis 3. This is at 1920x1200 using a GTX 680. The difference between the i3 and i5 is 40%. While this is not indicative off all PC games, it illustrates a growing trend of multithreading games for maximum performance. We will only see more of this in the future, especially with the new consoles moving to a multicore x86 architecture. Bottom line is don't buy anything less than an Ivy Bridge i5 or and AMD FX-8350.

Lastly, what type of budget are you dealing with?

I saw you had mentioned earlier you only had about £150 to play around with. I noted a few things on my earlier post but I figured I'd follow up. If you're intent on staying with what you have I'd really recommend an overclock if your board can support it. The Q6600 is very durable so the likelihood of having a problem is slim. You're actually more likely to have problems with your motherboard before the CPU starts acting up.

Anyway, I've noticed a few issues first. When running dual channel Ram should always have matching sizes. It's inefficient to supply one channel with 2GB and the other with 1GB. Secondly, your ram should ideally be running in sync with your bus speed. Since your default bus speed at 2.4ghz is 1066mhz, your Ram should be running at 533mhz, not 400. Always link and sync your DRAM to your Bus speed. In this case since the board only supports DDR2 up to 800 so a 2:1 ratio would be ideal.

As for overclocking, make sure you have a good CPU cooler and see if you can get it up to 3.2ghz. With these processors this would be accomplished by raising the FSB speed to 1333mhz. This should be easily achieved, since your board was designed to handle the 45nm processors which utilize this setting by default. Remember to sync your ram to this as well. That means raising the DRAM speed to 667mhz.

In short, here's what you should do, to maximize what you've got at the moment.

1. Upgrade to Windows 7 64bit. Your existing product key will work for this, you just need to get the installation disc. This can be found easily online as an iso download.
2. Make sure your DRAM sticks match. Brand isn't as important as Capacity and Voltage. 2, 2 Gig sticks should be enough for now.
3. Get a good cooler for your CPU and overclock to 3.2ghz by upping the FSB Speed to 1333mhz. Remember to sync your DRAM speed to 667mhz.
4. Get a decent video card. The Radeon 7850 or GTX 660 should work great. Make sure you get a video card with no less than 2GB of video ram. This will help down the road. The Radeon is a particularly good deal at the moment since it comes with both Bioshock Infinite and Tomb Raider for free.

There is more information related to building a new computer and the effects of switching processors in my earlier post, but if you can OC your Q6600, there is no reason to move to an i3. Hope this helps.

The GTX660 and HD7850 are pretty much the same in performance, each edging out the other depending on game.
Bear in mind neither will give its full performance in the existing system, they'll both be held back by the CPU.
I suspect you'll carry this over into the new build later this year so a good warranty should be a top priority.
A few UK links: Scan, Ocerclockers, Pixmania, Dabs, Novatech, CCL, Ebuyer, Aria and Misco...Amongst others .
Check before you 'add to cart' that your existing power supply has the right number of PCI-E power leads!
As has been said, the Q6600 has good overclocking potential, you might be surprised how much extra performance is lurking in that tiny piece of silicon.
The Internet Rumour Mill suggests Nvidia my release a new generation of cards in a few months, a common feature of PC hardware where there's always a better deal tomorrow!

Good call - I was going to suggest sell it and starts from scratch. You will need 4GB to run today's games, btw. To answer your final question - the best bang for buck in that range is the GTX 660 - but an HD 7870 XT (Tahiti LE) or GTX 660Ti would be even better if you can stretch it.