I'll have a look at Tiger. Remember, though, nearly any decent computer can be a music computer. RAM is king and 2 gigs worth is fast becoming the bare minimum. Plenty of fast storage is also important and I'd go with a SATA HD, better yet, two them or even three, with at least 80 gigs each. A Pentium 2.8 ghz processor would be a good start, faster if you can afford it. All this means little, though, until you get your OS, preferably WinXP, optimized for audio production and thats the real secret. Optimizing your OS will make a huge difference from a non-optimized system, but I'm still learning how to do that, so I cannot offer any advice on that yet, sorry.
I know nothing of macs, so I'll keep my pie-hole shut there too, although I know much of the music industry uses them and will never change to PC. There's something to be said for that. I will say, however, that your choices of software, audio and otherwise, are far greater on the PC platform. Cheaper too.
Thanks for the links to Tiger. =)