I took out my Voodoo 2s thinking it was causing some problems (it was something else). Now I put them back in and SLI no longer works. I have tried completly uninstalling the drivers and reinstalling them numerous times, and I can only get one card or the other to work. Any ideas??

How do you know that the Sli is not working ?

FPS is lower, 1024x768 doesn't work, and I don't get those scan line type things when you move too fast..

Have you tried this?
Open regedit.exe and look for:
[HKEY_LOCAL_MACHINE\SOFTWARE\3Dfx Interactive\Voodoo2\Glide]
put this string in:
SSTV2_SWAPBOARDS
set value to 1
exit regedit.

It works, thanks man.