Well, the thing with audio recording is that if you really really want to do it right, you need to spend the money. If you just want to do simple things, then almost any computer will work. On the Mac side of the pond, any PowerMac with an audio in and a copy of Coaster will usually do the trick. Hard drive space is critical as sound files become HUGE, but that's just the nature of the beast. If you plan on starting small and building a more advanced computer recording system later, go with a PCI based PowerMac, probably a G3 or better, lots of RAM, stay away from an OS X system for now, the audio tools for it will be coming, but they aren't here yet. Stick to Mac OS 9.2 or earlier. Even a System 7.6 Mac with the propor software is a very stable and powerful work station.

One thing to keep in mind is that currently no new Macs come with an audio in- if you buy new you'll have to buy a USB, FireWire, or PCI based audio capture system. These can be faily inexpensive or very very expensive. On the other hand, you'll get a fast, stable computer with a lot of hard drive space and a CD-RW drive built in.