Question : Nvidia 8500 - Medion pc

I have a Medion MT 475G pc - that is about 8 month old. It was originally installed with Windows Vista and a NVidia 8400 grafikcard.
I wanted to use XP instead, but everytime I tried to install the 8400 the screen goes totally black and in the right corner of the screen the curser is just placed. I can restart the pc, and I have a picture agian

I thought it was because of the wired 8400 grafikcard from medion, so I now tried with a Nvidia 8500 - but also there, the exact same error.

What is wrong - is it somehing in bios that is wrong or why is this so wired this medion pc

Answer : Nvidia 8500 - Medion pc

Found the XP driver on medions homepage