I don't think Diamond's video card division was absorbed by anyone. They pretty much faded away. I assume from the name that the card is an S3 Savage 2000. There should be native support for this old chipset within most modern Linux kernels. For 3D/OpenGL drivers, you'd probably have to hit Sourceforge because I don't think S3 would have drivers available for a card that old.
If it's an NVIDIA card (Riva TNT or better) the current Linux drivers available from www.nvidia.com
will work. Check out the NVIDIA Linux forum here for download and installation instructions.
BTW, some mod want to move this to the proper Linux forum?