Jedi Knight II uses OpenGL drivers. My Voodoo 3000 refused to run the game at all (black screen) until i downloaded the Wicked3D OpenGL drivers (
www.wicked3d.com).
I don't know if they support other cards besides 3Dfx but these drivers solved my problem...
Update your card's drivers first, install all the latest patches for these games and check out Wicked3D.