How much am I bottlenecking?

What resolution are you planning to play at? You can always lower the graphic setting to make up for the bottle neck with the resolution. However, the logic of it will stilll be that the gts 450 isn't being used to its full potential.

You're bottlenecked a pretty good amount sorry to say. How do your games run?

A CPU bottleneck means that the processor is limiting the card. Lowering graphics setting will do the exact opposite of what you say; it will put less strain on the GPU which is already not being used as much as possible.

@OP: A P4 is going to bottleneck a GTS 450 a rather large amount, especially at low resolutions. It would be a good idea to replace your motherboard/CPU/RAM. It doesn't need to be that expensive. Even a $50 CPU is several times better than your current processor, a cheap motherboard is around $50-60 and 4g of DDR3 is about $25. If you can afford it though I would recommend spending $100 for a quad-core processor.

Well, on games like TF2, CSS, you know, single map-multi-player games, run quite well.
It has TONS of problems with other games though.
For example: GTA4, I have everything on the LOWEST settings, and the render distance is VERY close, yet I still get FPS lag during some parts.
But, I can play Left 4 Dead 2 on all the highest settings with no FPS lag at all. (Besides during hordes)

Well, I was thinking of REALLY upgrading my Mobo/CPU/RAM
Here's what I was aiming at...

Motherboard - http://www.newegg.com/Product/Product.aspx?Item=N82E168...

CPU - http://www.newegg.com/Product/Product.aspx?Item=N82E168...

RAM - http://www.newegg.com/Product/Product.aspx?Item=N82E168...

LOL that is definitely an upgrade. You should see a huge difference going from the p4 to the 2500k. What resolution do you play at?

Uhhhhhh...... 1600x900?

If you can afford an i5-2500k then it's definitely a great choice if you are going to be overclocking.
Here is a combo with the CPU and the same RAM(different color?) that will save you a bit;
http://www.newegg.com/Product/ComboDealDetails.aspx?Ite...
The motherboard also seems a bit pricey for microATX. Do you need it to be mATX to fit in your case?

No, I'm pretty sure I have a mid-ATX(7.25 × 16.00 × 14.25 inches)
And thanks for showing the combo.

This motherboard is very similar but ATX with more slots for expansion;
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
It's also $21 cheaper.

Alright I'll be goin' with that one.

Have you considered upgrading the card or getting a second for SLI?
One GTS 450 will be passable for 1600x900 but not particularly good but two would do very well and your new board does support SLI.
Are you getting a aftermarket cooler for overclocking the CPU?

As for the SLI'ing, yes, I will get another GTS 450, it'll do exactly what I want it to do.
And, maaaaaaybe I'll overclock the CPU, but not too much maybe to a 3.5, so yeah, I might get an aftermarket cooler.

That was my point when I ask about resolution. Another option is to sell the 450 and grab a 560ti or 6870 or better.

As much as I like to save other people money, I also like to spend it.

My advice is to take your old system and sell it along with the GTS 450 and get yourself a GTX version since that Core i5 won't even break a sweat running the GTS.

A few options:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

And, do you guys think this ( http://www.newegg.com/Product/Product.aspx?Item=N82E168... ) PSU would have enough power for the dual
GTS's and the i5 and mobo?

3.5ghz is nothing. These processors can easily get over 4ghz and usually 4.5ghz. You should decide if you'll be overclocking before buying. The only actually advantage of the K series is that they can be overclocked and the non-K chips are a bit cheaper.

It definitely would but it is much more than you need and quite expensive. This is a good PSU and will also easily cover your needs for less than half the price;
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Just my 2 cents again but SLI is not a great idea over a single GPU, the extra power it requires and heat it produces is only the first issue, some games do not play well with SLI and drivers to fix the issues come out slowly and in most cases 6 months after the game was out. I have ran SLI many times in the past and every time I end up telling myself never again!

You should also save some money and get yourself a 650w power supply, the 850 is way overkill!

Well, I currently have a 600W. http://www.newegg.com/Product/Product.aspx?Item=N82E168...
Would that suffice?

Well, as for the Graphics card, mine will do what I want until I feel the need to upgrade, so thanks for telling me that SLI is NOT the way to go.

And as for the Power Supply, I now realize, yes, it is too much, but I already have a 600Watt, so jumping 50 Watts isn't so great.

What about a 700-750?

Yeah, that PSU should be alright. It has 504w on the +12v rail. SLIed GTS 450s max out around 170w at reference and 215w with a high OC. The i5 is a 95w CPU, about 125w with a high OC. So even with everything OCed a ton you should have over 150w left for the rest of the system which is fine.

You can still use your 600w power supply, it will work fine with the rated power.

The power supply manufacturer can tell you whether it is rated as actual power or something false but since it's made by HEC I don't know much about that company although for the price you paid I would guess they are reputable.

If you had a 600w power supply you paid $25 for then I would say hell no!

Here is a review of the PSU;
http://www.hardwareheaven.com/reviews/957/pg1/xigmatek-...
It's pretty good.

Well, the 12V+ rail is the whole reason I got the damn thing.
When I got my GTS450, I have a 500W Rosewill, but it only had 20Amps on the 12V+(The Graphics Card required a minimum of 22Amps), so I needed a new one, so I found this thing for a good price, with good reviews.

Well, you seem to know your stuff when it comes to Graphics Cards,(I'm not so up-to-date with them) so far, out of all the Graphics cards I've tried, here's what I've found.
AMD - Never tried 'em
ATI - Hates my computer
nVidia - Works great!
My top producers have got to be EVGA, ASUS, and Galaxy.

So I'm looking at a GTX460 by one of those companies.
Which one would you suggest?

AMD/ATI are the same company. AMD bought ATI about 5 years ago. As of the current series of cards they simply dropped the ATI brand altogether and just use AMD.
For a GTX 460 I would get this and give it a nice OC;
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
However I REALLY suggest not taking one person's word that you shouldn't consider SLI. A single card is certainly simpler to deal with but tons of people use SLI without much of an issue. The heat/power aspect brought up isn't all that relevant for a lower mid-range card like the GTS 450.