Right click on My Computer and choose Properties, then the Hardware tab, then the Device Manager button. Click on Display Adapters and then double-click on your graphics card. Now click on the Drivers tab.Your nVidia drivers should be *at least* more recent than the release of DX 9.0c -- that is, after Aug 4, 2004. If they aren't, get and install a fresh set from:
http://www.nvidia.com/content/drivers/drivers.asp
If your drivers are recent, let us know and we'll try something else. If not, update and tell us if it helps.