GPU recommendation

Hi, may i know which is the most suitable upgrade gpu for my pc? Here is my pc specs: Core 2 duo e7400, 2gb ddr2 ram, 320 hdd, normal 450w (no 6+2 pin) psu and screen resolution 1366 x 768. I'm currently using win xp and planning to upgrade to win 7. My current gpu is 9400 gt and thinking of upgrading my gpu to hd 6670 or gt 640. Any other recommendation for gpu that not going to bottleneck my cpu cos am not planning to upgrade anything else beside gpu or ram. Nvidia or ati gpu is better for light gaming? My budget for gpu is below $80.

Thanks and have a nice day!

If you can stretch your budget by a few dollars for shipping and can wait for a mail in rebate, this one is $80 after MIR + shipping

http://www.newegg.com/Product/Product.aspx?Item=N82E16814150661

SAPPHIRE Radeon HD 7750 http://www.newegg.com/Product/Product.aspx?Item=N82E16814102969

I believe the 6770 is faster than the 7750. I'd go for that probably over the 7750

EDIT; Well assuming the 5770 is the same as the 6770 (Which I believe is true performance wise), they're about the same I suppose. Go the 7750 I guess for slightly lower power draw, and no need for the PCIE connector.

7750 seems to win out barely at lower resolutions; but loses at 1200p and above.

7750 actually consumes a lot less power and is just barely slower than the 6770.

The 7750 will probably be best for the OP.

In fact, here's one that's the same price as the 6770 I suggested earlier, just costs a little less for shipping: http://www.newegg.com/Product/Product.aspx?Item=N82E16814131481

hmm..seems like everybody suggested 7750 1gb ddr5..is there a lot of diff between 6670 1gb ddr5 and 7750 1gb ddr5?

Kelvin just be careful about your PSU, a cheap PSU can wreak havoc on the whole system. If you are looking to upgrade I would make sure you either have or get a quality PSU first. This is a good upgrade for you if you find your PSU to be lacking.

Thanks for reminding bout my pc PSU and i did thought about it. I know there is a lot to upgrade but it's not about 1 pc and actually more than 15 pcs and i just try to find the lowest cost for upgrading.