I missed out on the voodoo2 days with my first real 3D card being a V3 3000, so in order to make up for missing out, I have the following parts coming for a retro gaming machince:

PII 350
ASUS P2B
128MB PC100
1 BlackMagic II
1 Diamond Monster II
Matrox Millenium

my questions are:

will these cards work in SLI?  If not, what do i want for an SLI setup?
what OS is best for playing old glide games?
what else should i know about a setup like this?

..you dont need SLI for such an old machine.a single voodoo2 is enough,and it should work with no problems in that machine.bad thing is that no one really knows if those two v2s will be able to work together,mismatched SLI is usually some major pain.if you really want to go for voodoo2 SLI you should use identical cards and at least a p3 600MHz cpu or better.you will need one pass-through cable and one SLI cable.the best os for voodoo2 is win98se of course..(check here for some nice info )

ps47; you're forgetting that should he run a SLI setup on this machine, he could probably do maximum details or 1024x768 without a drop in framerate.

correct.he will get acces to 1024*768 resolution,but his performance will NOT increase (at least not significantly).the CPU is simply too slow,it just cant feed the voodoo2 SLI with enough power.there was a nice little test about this somewhere,wait a sec,got it.and I must agree with it,I have tested v2 SLI on my k6-2 333MHz,and the speed increase was something like 0-10%.things started to get better with a p3 600 CPU,but the real fun has begun once I installed the v2 SLI in my barton 3000 machine..its the same situation like today with gf6800SLI,you will need a much more faster CPU than currently available to see the gf6800SLI true power..

I hope you can get those 2 different Voodoo2 cards to work correctly in SLI. Also, the Voodoo3 3000 was almost the same as a Voodoo2 SLI setup so you really didn't miss anything, well, except for being able to say you have a Voodoo2 SLI setup...
Here is my Voodoo2 SLI system:

Asus P3B-F Intel 440BX chipset
Intel PIII 650
128 Mb PC100 Corsair SDRAM
30 Gb Maxtor DiamondMax 7200 RPM HD
Mitsumi 48X CD-ROM
Windows 98se
Diamond Viper 770 Ultra 32Mb AGP
Diamond Monster 3D II 24Mb SLI
Sound Blaster AWE 64 Gold
MS SideWinder Precision Pro Joystick
US Robotics 56K V.90 Fax/Modem w/voice
KTI KF-230TX 10/100 NIC