There are some beta/tweaked XP drivers
available here for the ViperII / Savage2000.
You can try them, they are pretty much the best option at the moment but they aren't perfect and there are no guarantee's about how well they will work. At best normal windows and DirectX will work, but there will be no OpenGL (which is bad as that was what the card was probably best at).
Your other option is to buy a new card or just stick with Windows 98/ME.