Your issue is unrelated, then, and the one described here:
http://forums.3drealms.com/vb/showthread.php?t=20667
Unfortunately, that card is not among our officially supported cards, so it can't be expected to run the game properly. You may have some luck, though, upgrading to the latest Catalyst drivers that support the card. I think they cut off somewhere around
https://support.ati.com/ics/support/...estionID=19549 but I'm really not sure.
Thanks,
Rich