don't forget to check the input level in the audio-preference pane, before you digitize a whole tape (that happened to me once...), and you might want to take a look at this:
http://www.versiontracker.com/dyn/moreinfo/macosx/26293 ,
it's a transscription software, a roommate of mine used it for some interviews, and he was quite happy with it.
edit: too late...