I've actually used Glidos
to run Redguard on my XP machine, so I know it can be made to work. Problem is that was 2.5 years ago so I don't remember the gory details. :? One thing I do remember is you actually have to purchase Glidos (the Voodoo emulator) if you want to continue playing the game after you get it working. The 'trial' version keeps a spinning logo on top of the game as it plays, from what I recall. Information on setting up Redguard with Glidos is here
in case you hadn't found it yet.
It does specifically require a 3dFX / Voodoo card, but I'd think you'd have some luck on a machine that doesn't have a 3D graphics card by installing the 'software version'. Trouble is it would look like crap. Best bet to me would be an old machine, running Windows 95 or 98 and an actual Voodoo card. I wonder how hard it would be to find one nowadays? I think I've got an old Pure3D card gathering dust somewhere...