You need a PC with a graphics card that can display on three monitors at once (Nvidia do the GTX 660Ti, 670 and 680, it's possible even the 660 and/or 650 do too but I wouldn't bother as they're too low-end to be any good at that resolution, I don't know which AMD cards do it though but there are some) or two cards in SLI or XFire (like two 570s or something, it basically means you connect them together to get essentially dual/triple/quad-core graphics processing), but once you've got that and your three monitors - they must all have the same resolution (not necessarily the same size though) if you're using an Nvidia card - just plug them in, go to the Nvidia control panel and turn Surround on. After that your surround resolution will be selectable in games.
Other options include the Triple Head2Go, SoftTH (requires two graphics cards, but they don't have to be the same) and... I think that's it. Don't ask me how to use those though. I personally use a GTX 680 with three 1680x1050 monitors and it works almost flawlessly. The only problem I have is my taskbar acts up sometimes.
It's still not cheap but it's more versatile than buying two more PS3s just for one game. I think SoftTH is probably the cheapest option but I don't know how good it is. Oh and you'll definitely want a wheel if you haven't already got one.
