I found this on eBay and it's on the way. Is there anything special I need to set it up? I don't think it will have any drivers since it's used. I currently have a single Diamond Monster Voodoo 2 using the driver on the CD that it came with (I'm the original owner). I know there have been some drivers developed for 3DFX over the years but haven't messed with them. Any suggestions or help would be appreciated. The 3DFX cards are PCI. I have an old Gateway P4 1.8 gHz Socket 478/850 Chipset with 512 megs RAM. The graphics card is a GeForce Ti-4600 128 meg AGP. PSU is 250 watts. I'm running Win98SE on this box.
As far as i know, you don't need anything special. Also; i don't know if you can put them on SLI either. Now for drivers, try this: http://drivers.softpedia.com/progDownload/3Dfx-GlideXP-Final-build-1016-Download-265.html
The set of cards I'm getting were designed as an SLI setup out of the box. Here's a link to see what they look like: http://www.3dfx.ch/gallery/v/3dfx_collectors/collectors_eyeq/sold/V2/Diamond+Megamonster+3D+II+SLI-Set.jpg.html I'm not sure what you mean by saying "...don't know if you can put them on SLI either." They were designed specifically to be installed in SLI.
I used the newest driver provided by 3DFx for my Voodoo 2 cards on Windows 98 SE, it corrects some issues and supports the latest Glide API supported by the card. I suppose you have 2 monsters with 12MB on each? As for SLI, the only thing special that you need is the grey ribbon cable between the cards and only using one short VGA cable in the same way as you do with a single Voodoo2.