All you need to make high quality audio recordings is an iMic, which is a device that plugs into your USB port and allows you to connect microphones or a line feed(such as the output from a tape deck) to your computer, and Rogue Amoeba Audio Hijack which will allow you to record and edit any kind of digital input(free demo, and only $16 if you like it)--

The recording quality for iMic is a lot better than the built in input(which is an option)--only thing, after you've converted the tapes to digital, and burned the CD, you should keep the tapes--don't ever throw away the original source material, nothing else will ever be as good--