So what do I need to get started?

You need:

A computer (preferrably a G4)

A soundcard or Firewire/USB-based audio interface (this takes allows you to record audio --guitar, vocals, whatever-- into your computer). Mac has a built-in soundcard, so you could use that, but if you want to do high quality, best to buy a stand-alone soundcard/audio interface

An external mixer to monitor/route your signals

A good pair of studio headphones and if you have money, external self-powered monitors to playback.

A good software sequencer (eg., Logic, Cakewalk/Sonar, or Pro tools)

that's it

Thanx a lot!!