Oy, sounds bad. I think that your particular version of ATI card had a transparency issue that was basically unsolvable for our compatibility programmer. Suggestion? I hate to say it, but you may have to bite the bullet and go buy a new video card. My guess is that you'll wind up happier with a new card anyways - your machine should be plenty fast to run today's games; if games are running slow, it's almost definitely your video card is too old.
I tried looking around online for some cheap Voodoo1 or Voodoo2 add-in cards that I'd give you pointers to, but I can't find any
If you can find a used Diamond Monster 1 or Monster 2 card somewhere, it's worth the money if it's less that 25-30 bucks or so. Jeez, I have 2 or 3 of them lying around here at the office.
My suggestion is to get an add-in card because that's the cheapest; you can find a really good Voodoo3 card for under a hundred bucks nowadays, but that would require replacing your card. Voodoo1 and 2 cards are simply added into your system, using your existing video card for windows, and the add-in card for games etc.