HD 2900 XT Performance problems

I installed my HD 2900 XT about 3 weeks ago. I began to notice that it wasn't getting enough power in the first week, so I ordered a dedicated power supply to get it more power. After I got it all hooked up, I ran it, and the performance and framerate was still just horrible. I noticed it worst in partially Halo 2 Vista and very very badly in Lost Planet. In lost planet it was so bad that it even said that I needed to improve my system requirements in the middle of the game. Does anyone have any idea why this card isn't working for me, or did I install it incorrectly or something? I really want to get this working before crysis comes out. My specs are: Processor is an E6600 Dual Core processor, which I over clocked to 3.2 GHz and it was 2.4 before. My video card is the HD 2900 XT. I have 500gb of hard drive space. My PSU is 600watts, and my dedicated power supply for the graphics card is 450watts in case i want to do crossfire. Here is my mother board http://www.newegg.com/product/produc...8 2E16813121059.

And this is my case http://www.newegg.com/product/produc...8 2E16811133021.

I am also running it on vista, which I here isn't that great for gaming YET.

Anyone know whats going on here?
Thanks,
Zman4700

I would like to help but the links are broken.

Could you list the specs manually? Please include the PSUs, the driver version you are using as well as the Vista build.

By the way, those links work