"Onboard" video cards can be a little tricky to get working correctly in linux.
This; http://mail-index.netbsd.org/netbsd-...7/30/0013.html link has a
driver for the s3 prosavage.
I haven't used this one myself I have set up video, onboard and pci
You might try some of the things the link above suggests (It's for both bsd & linux)
Let us know how you make out.