What exactly do you want this PC to do???? Will you be running CAD, Photoshop, Quake and SETI computations at the same time??
Most commecial software today cannot take full advantage of the hardware thats currently available! A 2.2 Ghz CPU with 1GB of DDR Ram, a MB with a 500MHz bus, a 64MB 4x AGP card(w/DDR) and 2 80 GB scsi Hard drives (10,000rpm) would probably do you fine if you want the absolute fastest thing available, but even then. Id say in about one (two) year/s, If you could find, and use, a piece of software that would make this hardware obsolete, Id be REALLY suprised. Pro tools and sonar both can run great on half of whats listed, if not lower.
If you really want to go for the gusto though, buy a Server with 4 xeon processors and 4 GB od RAM. I dont know what you would do with it, but it would probably satiate the gear yearning your feeling.
Todd