I'm a happy PC to Mac switcher and I've got to say, if audio is your thing and you can afford what you need in mac gear, then it is the best way, period. I've been using
my Powermac G4 dual 1.25Ghz (1gb RAM) for almost two years now I believe and have never been happier, more stable, or as fast as I am now.
As far as multitracking software goes, I'm a fan of MOTU digital performer. Probably because I use
a MOTU 896HD firewire interface. I find it has the easiest interface to work with and also integrates seamlessly with my gear.
Logic is also nice, as is protools. Cubase and many of the others are also available.
If all you need is 8 tracks of audio, go with something like
MOTU AudioDesk. It's basically digital performer minus all the midi and sequencing tools. Great multitracking app though, and I love the interface. Check it out...
http://www.motu.com/english/motuaudio/audiodesk/body.html
Anyways... If you need a bit more, check out Cubase SL. It's basically the same idea as audiodesk vs. digital performer except it's big brother is Cubase SX.
For 8 tracks at 44.1 16bit or even 24bit 733 G4 should be plenty granted you have a good amount of ram. Hell, 96khz 24bit will probably run fine. My dual 1.25 runs smoooooooooth and quickly doing 36 tracks of 24/96 audio, so I'm assuming half of that will still do really well, as will 733mhz. Keep in mind, the powerpc platform and the wintel/amd platform are completely different as far as clock speeds go. a g4 1.25ghz runs circles around a p4 2.5 or even 3 ghz in most cases. Don't even start with me on the G5s. Oh my how those are amazing.