CASSETTE TAPES TO COMPUTER

What model iMac do you have and what OS version is it running? You should consider purchasing Roxio's "Toast," which includes a program for importing audio from various sources, such as a cassette deck. Typically, the software has editing options, including the capability of reducing hiss from playback of cassettes not recorded with Dolby Noise Reduction technology.

I also use Audacity for this. This can convert the audio files to AIFF for iTunes.