Problem with ATI Radeon X850XT 256mb Video Card PCIe

Hello all--happy to be joining you all at this forum! This may be a bit long, so brace yourselves....Please excuse the typos =O

So let me start off with my system specs:

Gigabyte GA-K8N Pro-SLI Socket 939 MB
Aspire 550W power supply
AMD Athlon X2 4800+
2 X 74 GB WD Raptor SATA RAID 0 HDs
Lite-On DVD/CD combo drive
2GB dual channel Corsair memory
Floppy Drive
ATI (manufactured by ATI themselves) Radeon X850XT 256mb PCIe

So I have been having frame rate issues. I used to have a computer that was not as nice as this one with a ATI Radeon 9800Pro 128mb AGP video card and a slower processer with half the RAM.

Warcraft 3 used to run really smooth, and I had very little problem with doom3 on high settings etc.

The frame rate thing seems weird. For instance, in warcraft3, the unit photos and everything SURROUNDING the action of the game is crystal clear. However, the units move choppily, and to my dismay, much less crisp than my last system's card ran the game.

Furthermore, I have a friend with a comp that is much slower than mine spec wise, and he also has a slower video card, the ATI Radeon X800, and his computer runs World of Warcraft on highest settings fine. I can't put my settings up all the way on the game, and if anything I have to put it to medium setting to get somewhat clear movement. Even Homeworld2 had some pathetic frame rates too....

Here is what I have done--put the card in different slots, reinstalled the drivers, updated the games, updated the drivers etc etc. I even have a new MB from the company I bought it from just in case it was the MB...

Currently I am testing an ATI X300 SE PCIe in this computer, since I RMAed the X850XT PCIe for a replacement. I still have pretty laggy frame rates even with this X300 SE PCIe and I am wondering...

Do you all think that my motherboard, since it is SLI compatable and has an NForce chipset, is performing poorly due to the video card being ATI? I don't think this is a problem, but I have tested to different ATI cards in my MB and I believe they are performing sub-par, so I am starting to wonder. Is this a common issue or something for ATIs to perform poorly in these types of MBs?

Thanks a lot for your help all =)