Nvidia 6600gt driver trouble, please help totally out of ideas.

Earlier this week I purchased a nvidia vc and power supply to support it (450w). After installing the card and running the latest video driver I seem to be having major problems while playing World of WarCraft. The game loads fine but during game play my character tends to freeze or background flickers and disappears. While reading other forums similar to this problem many have one thing in common, a Asus sis chip set AMD board. I've re-installed nvidia drivers and dl'd sisagp update from sis.com.tw and still game play is horrible. Could really use some help...thank you.

Asus A7s8x sis board, amd 3000
nvidia 6600 gt 128
512mb
450w ps
120 hd
3 fans since nvidia card tends to run at a high temp.

Howdy! Welcome to TechSpot

Try rolling back the drivers to 71.89
@ the top of this page is a driver link that should
have if not try Gur3d
Hope this helps, if not post back we' try ta help you.
G'Luck