i would definetly get a sata raid 0 hard drive setup and 2 Gb of ram. this will make your comp work faster with those large audio files and multi-track recording programs. next, go to a music equipment store, maybe one that specializes in computer music hardware, and look at the sound cards, recording software and midi interface. tell the salesman your plans, budget etc. and he should be able to help you.
Pentium 4 3.0Ghz, 1Gb pc3200
BFG 6800gt, samsung 19\"
Audigy 2 ZS, TruePower 550 watt
3Dmark05 - 4750, Aquamark3 - 59 200