I got this old computer from a friend with a Voodoo1 Monster in it but no other gfxcard. Now Windows refuses to accept any other resolution than VGA, even though the 3Dcard definetly works. Tried many different drivers... Anyone experienced this?

If it's a Voodoo1, then there's definitely another Video Card in that System (likely onboard Video)

The Voodoo1 is a 3D Only card, therefor it needs a 2D Video card (any).
Since the Problem you're describing comes from your Onboard / 2D Video card, the 3dfx plays no role in it.

Chances are, you need a proper Video Card driver for whatever you got as a 2D Card.

The Device Property page will list the Display adapter (if a Driver is installed), otherwise it may read "Standard VGA".
If you're not sure what Model/Chip it has, either consult the Motherboard manual or download and run Everest (or any other Hardware analysys Tool)

Thanks a lot! I was a little confused but with the right chipset drivers it works!

cheers
/Aron