Has an audio in socket on the back.
Connect your Cassette or Turntable output, probably through a pre-amp, into it.
Use a program like Audion, or the one that comes with Toast, to record and clean up your tracks.
How does one go about getting Cassette or Turntable records analog audio into the imac G5 ? is it easier to buy Archos Gmini with line in ports and digitize that way and later transfer files to Mac via cable? thanks