600 Mhz? is that a G4, if it is a G3 forget it you will pull your hair out. i have XP Pro running on my 500 Mhz TiBook G4, and its slow. i also have a (new) alienware 3 Ghz P4, so i guess saying it is slow is an understatment. but that is because of my place of reference.
as far as running audio software emulated, you will not be happy. i have used a dual 1.25 Ghz G4 at work with Win XP Pro and it was usable, but not speedy. VPC 6 just came out, wich helps with emu of XP Pro a lot. but bottom like is XP is SLOW under VPC, especialy under OS X. if you are going to run XP on the Mac, reboot into OS 9. the reason for this is OS X does not allow apps like VPC to hog the CPU like OS 9 does, and VCP NEEDS to hog the CPU. u can 'renice' VPC in OS X, that helps a lot. there are premade AppleScripts to do that, if you want one i suggest the excellent macosxhints site and board. Win2k in VPC is a lot faster, if the software you are using will run under 2k.
you people that bash Mac's discust me. i dont bash Windows, or Linux, i just use them. and ya know what, being able to use them all is a lot better than just being able to use one OS. i wish there was a Mac emu for Windows that was as nice and full featured as VPC is.