I don't see how splitting one single into two will give him seperate displays. It should just mirror it. I've never used one, so I very well could be wrong. Are you looking to game on all three at the same time, or just view pages on all three? If you are looking to game, I'd replace the motherboard. Get one that supports has two or more 16X slots. Buy two video cards, and your done. If you just want to view pages on them, or game on one with other pages up so you can check email/IMs, then buy a video card that fits in the 1x slot.
What OS are you using? If your using XP, your fine. XP can load and use two different video drivers. If you've moved to vista, you'll only be able to load one, so the one I linked wouldn't work. It could, but you'll need to dump the 7900 for something newer.
I purchased the PCIE-1x video card. I now have 2- 17" dell 1704fp monitors on either side of my 24" dell 2407wfp monitor. Each 17" is turned on its side. Works perfetly with the software included by both ATI and nVidia.