Asus R 9600xt problems in Planetside

[Cichy]

I just purchased Asus Radeon 9600xt to replace my old gforce4 mx4.

The problem I'm having is that entire system freezes up after 1-5 minutes after playing Planetside and other games such as Gunmetal (which came with the card) and DeuxEx2. I'm forced to reboot the system.
Surprisingly Call of Duty is the only one that doesn't freeze up.

I uninstalled the drivers that came with card and installed the latest catalyst driver off the ati website but it didn't help. Then I tried older catalyst and asus drivers but still the system freezes up. I ran a virus scan to be sure but the system is clean.

I'm beginning to think that the card may be defective but that doesn't explain why Call of Duty runs fine.

Some system specs:
VIA chipset mobo
Intel Celeron Celeron 1700
512mb ddr ram
Windows XP
Montego Bay A3DXtream sound

Any help would be greatly appreciated.
Thanks in advance.