thanks for the reply.
I proceeded by installing Win 7 RC1 with the X800 GTO. Currently there is only RC1 installed, no other OS. The HDD consists of only one partition ( 1 primary ).
I wasn't able to test the card with vista as I jumped from XP Pro to 7 RC1 now. There is a CD though that came with the card, which is labelled "Vista drivers". So in theory it should work.
Really glad to find some help here