Try searching their knowledgebase, see if you can find any useful info there. Maybe try <A HREF="http://support.microsoft.com/default.aspx?kbid=822798" target="_new">this</A> page.
Also, you can try uninstalling ALL video card drivers, using the Uninstall Programs, <A HREF="http://download.guru3d.com/detonator-rip/" target="_new">Detonator RIP</A>, <A HREF="http://www.softpedia.com/public/cat/12/1/12-1-28.shtml" target="_new">Nasty File Remover</A>, and a registry cleaner. Then reboot and re-install the nVidia drivers. Its possible that the newest drivers haven't been passed by M$, and thats causing the problems.
Spec:
Intel P4 2.4B
MSI 645E Max-U Mobo
1GB DDR333
R9600XT 128MB
SB Live 5.1
Samsung 120GB
Maxtor 120GB
LG DVD+-R/RW
WIN2K PRO SP4