Normally the driver for S3 virge is included in the XFree drivers, but I am not sure if it supports accelerated OpenGL. It seems to be a quite old card (more than 5 years old, only 4 MB video RAM, but I can be wrong with this). I would suggest to upgrade to a more recent card, e.g. you can get Geforce2 - 4 cards for PCI too. Riva TNT 1 should be enough for Graal too if you can find that second-hand.
-update-
Ok I have searched some more. There is OpenGL for S3 virge, the homepage for it is at
http://utah-glx.sourceforge.net/. They say that it is only working for XFree3 (quite old) and it's not included/tested in the current XFree4, but it maybe work.