It's almost certainly the card's fault. One thing you might want to try to see if you can't get some of the stuttering/freezing in your games to stop, though, is to make sure you have done all the steps in dual-core help link 2 (see my sig), and then see if there is a fix available for you in this thread
over at Hard Forum.
But yeah, axy1985 is right, you should RMA that video card for a replacement if reinstalling the latest drivers doesn't solve your problem.
Hope all this helps.
AMD Opteron 165 CCBBE (2.7GHz @ 1.35v)
DFI CFX3200-DR (07/28)
Kingston HyperX DDR500 (3-3-3-8-1T)
Asus Dark Knight Radeon 4870 1GB
2x 74GB Western Digital Raptors in RAID0
500GB SATA-300 WD Drive
CoolerMaster RealPowerPro 850W
NZXT Zero full-tower case
Windows XP Pro SP2