An iMac is certainly capable of digital audio recording. Because of it's inherent limitations (small screen, no PCI slots, limited hard drive), It wouldn't be a good choice for a serious digital audio workstation, but the built-in AD/DA converters are more than adaquate for a 16 track home / project studio. There are also several cross-platform USB audio interfaces available now which offer higher even higher fidelity 24-bit audio, any of which would work on an iMac.
As far as software, some of the lower priced integrated MIDI / Audio packages I've had experience with are Cakewalk's Metro, which I think sucks, and eMagic's Logic Audio, which is pretty good, although has a rather steep learing curve. I'm not sure whether any version of DigiDesign's ProTools would run on an iMac, but it's great software.
It gets tricky when you start adding external interfaces, because you really have to research which applications will be compatible. This technology is evolving so quickly, especially at the low end (home studio) level, that a lot of things haven't really become standardized yet, and Mac compatibility is sometimes iffy for supposedly cross-platform hardware.[This message was edited by Jerry Gleason on 10 September 2000 at 12:16 PM.]