|yeah jam said pretty much everything i was going to:|
there's little benefit in an SLI/crossfire setup. A single card will typically be a bit cheaper, perform about the same, draw much less power, and produce much less heat.
i'll recommend STRONGLY against the PSU you "found in a pile..." The PSU is one of the most important components, and a crummy one has the potential to damage ALL your OTHER components. The worst part is that a crummy PSU could start wearing away at the lifespan of all your other expensive components, long before you started seeing any issues. And by the time you started crashing or blue-screening, it could have already damaged some/everything else.
i would probably also recommend the intel chipset over nvidia.
Also, were you going to run XP Pro x64? Unless your OS is 64 bit, you'll probably only be seeing about 3GB of that 4GB of RAM. And if you're going to go with a 64 bit OS, i'd recommend Vista x64 over XPx64 for ease of driver compatibility and longevity of support.