Phenom system REALLY low performance

I recently scored a deal on a Gateway with a 300-watt PSU, and 1TB HDD. It also has a Phenom 9500 (I know, I've heard a lot of hate about it) and a Radeon HD 2400xt. My problem is that I should be able to smoothly play NFS Shift on lowest settings at 800x600, but it is so laggy, on Windows 7 and Vista. I need to know if there's anything that I can do to make this thing perform better?? I know I need a new GFX card, but I'm not willing to spend much more than $100. I also know that having a 300-watt PSU is a problem. Would I be able to power a GeForce 9800 GT with my PSU? It does have a 6-Pin power connector, and I was looking at something along the lines of these:

http://www.newegg.com/Product/Prod [...] 6814134066
http://www.newegg.com/Product/Prod [...] 6814162028
http://www.newegg.com/Product/Prod [...] 6814130518

Which one should I feel comfortable putting in my box? I see that two of them say no extra power req's, and one of them says 6-pin. I don't want to get one that I will have to send back.
Also, I know everyone says how bad Phenom 1's are at overclocking, but is there any way i could get it up to 2.4 or 2.5 with software? Any other way i could inexpensively boost my performance?

this is a great inexpensive Power Supply Corsair CMPSU-400CX 400w 30a 12v single line + sleeved cables

http://www.frys.com/product/5834953
http://www.newegg.com/Product/Prod [...] 6817139008

im using it with a phenom2 720 o/c 4830 3 hdd 1dvd 4gb ram with power to spare its 30.00 after rebate
you can't beat it he saig he's upgrading a prebuilt box wants to upgrade video card psu is to weak
corsair is a quality brand he dosen't want to spend much but always nice to have more 700w gonna cost
a few bucks?

ok, so 500W should be good? Will it have all the right plugs for my computer? Here are some in my price range:

http://www.newegg.com/Product/Prod [...] 6817162013
http://www.newegg.com/Product/Prod [...] 6817709011

I really have no idea as to which ones would fit, and which ones are reliable, but I really dont want to go over $30, am i out of my mind?


Also, I have been noticing a little bit of weird behavior, core 3, according to a gadget for the sidebar, is always higher than the other cores, why?

Ok, you really don't want to use one of those.

To the other guys here, what about this PSU?

http://www.newegg.com/Product/Prod [...] 6817703018

Or maybe this Seasonic 300 watt?

http://www.newegg.com/Product/Prod [...] 6817151059


To the op, keep in mind you don't just want to look at wattage, you want to look at the amps on the 12v+ rails, as well as the efficiency. When you look at say the PC power and Cooling unit for example, it's 27 amps on the 12v+ rail, which is more than the 2 you picked, and I believe they are both rated to be 80% efficient, which means out of their peak load, they should be able to continuously run at 80% of that peak load nearly all the time.

Here's another good deal, 50 bucks, but a 20 dollar mail in rebate and free shipping.

http://www.newegg.com/Product/Prod [...] 6817151059


I have learned not to go too cheap on power supplies. Right now I'm running an Ultra 650 Lifetime Performance Series rated at 38 amps on the 12v+ rail. That power supply is not the greatest power supply, there are better rated power supplies, but it's been a good unit for me. But to give you an idea how strong the corsair unit actually is, it's rated at 30 amps. So it's actually strong. Realize however, don't just look at watts. I've seen 500 watt power supplies that were only rated for 17 amps. So keep that in mind. Don't fry a board on a cheap power supply like I've done before.

So, how would I know if this http://www.newegg.com/Product/Prod [...] 6817139008 PSU (mentioned above) would work in my case? it is a Gateway GT5658E, specs on following link:

http://support.gateway.com/s/PC/R/ [...] Rsp2.shtml

And according to the THG Graphics card hierarchy chart, here:
http://www.tomshardware.com/review [...] 404-7.html

the 4850 isnt too much higher above the 9800GT, but I do see now how it's a couple tiers above. Is this going to make it so I can even play GTAIV??? or NFS Shift at decent settings? and that corsair will easily power my computer, and fit inside the case, with plugs for my motherboard, 2HDD's, DVD drive, GFX card, etc.? BTW, thanks so much for the help, it's greatly appreciated.

From my experience, buy a good, high quality PSU since we've already had 3cheap burn out wrecking systems. Go with Tagan or Corsair, they're the best from my experience.