mushy101: Another Bit tech link ;) (don't worry, I don't work for them, just find them invaluable to us brits)
[url=]http://www.bit-tech.net/hardware/graphics/2010/09/15/how-to-overclock-your-graphics-card/1[/url]
EDIT: Whoops, linked wrong.
Second EDIT: With a 300w PSU, I'd be really careful with the overclocking. Open up your computer fist, just the side panel will do. If the PSU is a generic, no name PSU, which should be grey and cheap looking, please do not overclock since you run the risk of blowing it up, possibly damaging the entire computer.
Just the name of the psu and it's specifications will do, or a picture.
Bbtufty: Yeah, overclocking didn't work, I increased some settings to see no change in FPS in game, and when I pushed them up a bit further the screen went crazy and I had to hard shut down. Looks like I'ma have to look around for a cheap 6790. Do the names before it really matter, like Sapphire and VTX, and how long realistically before I'm gonna have to look for a new card to play newer games?
Those names are the names of the companies who integrate, assemble, and support the cards. They may enable different features, or put different coolers on. Sapphire (and more recently XFX) are ATI's (now AMD's) first-tier integrators. Sapphire is very aggressive on price and usually first to market. XFX has a reputation for good engineering, tech support, and warranty service. There are many others, such as Palit and HIS, who cater to enthusiasts in particular; and mainstream integrators like Diamond, VisionTek, and Powercolor (which also sells as VTX).
The "6790" is a departure from AMD/ATI's numbering convention. Usually that would mean "sixth generation, mid-range (7) architecture, top of the line (90)". But it's actually the bottom of the "Barts" GPUs, being a cut-down 6870/6850, so it would have been numbered "6830" -- were it not for the "xx30" part numbers being poorly regarded. So they pretend it is the best GPU in the next series down from "Barts", when it is actually the least of the Barts line.
All that hot air aside, you are still going to need both a GPU and a power supply that will get you some satisfaction playing TW2. You'll need a good 500W power supply (with at least 34 amps at +12V), at least an Antec EA500D, for any graphics card that's worth upgrading to.
An nVidia GTX 460 (the 1GB models are the best) or AMD/ATI 5850 would keep you going for a few years. Unless you can afford an nVidia GTX 560 or higher, or an AMD/ATI 69xx (not the 68xx or 6790), don't bother. And I wouldn't go any higher than those with your CPU anyway: even though it's a quad core, it's one of the weakest quad cores on the market, and there's no upgrade path for it short of replacing the whole computer.