I've built several systems to play old games using voodoo2's in SLI. On the current system I just built the screen goes blank (black or grey) everytime a game trys to use Glide. I am trying to play Quake 2 and Need for Speed 2 SE on this system and I have downloaded the final updates for both games. Here are the system details:
Win98SE
PIII 850
440BX chipset
Matrox G450 AGP
(2) STB V1000 Voodoo2's in SLI
Cards are recognized and working fine in device manager.
Have tried clean installs of reference, fastvoodoo 4.0 and 4.6
Have reseated, swapped cards and checked cables.
Quake 2 runs in OpenGL using the matrox and NFS2SE will run in software mode but as soon as I choose 3DFX screen goes blank (grey for Quake2 and black for NFS) and locks and I have to reboot.
Any suggestions or diagnostics I can run?

Yep. Make sure they work individually. I was having trouble with my v2 sli also. Tried them individually and figured that I had a memory problem on one of the cards.