First of all I downloaded English version which should be installed on a english Windows Vista Ultimate. This did not work at all. The setup exited and said nothing has changed - do you want to reboot? Then Windows Vista popped up an error dialog stating that I needed to download a fix for Age of Empires - duh!
After a few retries, and after some error messages stating that I was not running Windows Vista - duh again, I gave up and downloaded the international version from the UK site instead. This worked perfectly!
Now I can switch back and forth between Vista Desktop and Vista Media Center without having the screen to flicker like crazy.
NVIDIA has some more stuff to do before the real launch of Vista to the consumer market. I really need to get the overscan/underscan to work like it did in Windows XP. I have about 5% of my plasma unused right now.