Silverblade33 pretty much described my system! I have XP Pro 64 bit. Asus P5B.

Get as much memory as the motherboard can handle. Remember what Seymour Cray (as in Cray supercomputer) said about virtual memory. "Memory is like an orgasm. It's much better when you don't have to fake it." :-)

Do not buy a Pentium, they are obsolete. Get an Intel Core 2 quad, or if you're rich get a pair of Xeon quads like in a Mac Pro. (The newer Xeon is the server version of the Core 2. The older Xeon is the same but for the Pentium 4. Intel likes to confuse us.)