tmj, its a hard decision buying a computer for music. I never liked the idea and it took me along time just to submit to software, but I eventually did and now I like it alot.
I use a plain ol' off the self Dell Core2dual, dual 1.86ghz Conroe, XP Pro with 1 gig ram and a 256mhz graphics card, I do plan on adding a couple more gigs of ram soon. Buy as much extra ram as you can afford for processing Fx's etc. reverbs are a ram hawg. I got my Dell at the outlet store for $556...one to do ...make sure you "optimize" your puter for "music" after you set it up. Sweetwater has great guide for that on their website. Good luck.