if it helps I am a musician that uses both PC and Mac for music making and production and Mac's are always my first choice.
D3v1L80y is right it's not the machine making music but the musician.
I have used mainly a G5 Power Mac for the last two years and I have never had problems.
I just switched to a mac pro (cough:some issues there...) and I plan to use macs for music as long as they are made
Making music on a pc, which I still do was always frustrating since there is always something that does not work and I always spend more time fixing, installing , fine tuning, then acctually making music...given that I don't make any music on a pc any more but just edit and mix pc projects.
I always hated updating and upgrading on a pc, thats why i still have my two old pc racks running cakewalk and sonar in their original form, I think i added only memory.
Most of the studios I go in work with mac formats and that helps alot too.
if you can afford a mac go with something that has plenty of ram if you like running alot of plug ins, effects, audio tracks...etc
My old G5 (2.0ghz 4 gigs) never complained at anything I threw at it and they are fun to operate.
I belive macs are the way to go ....