Does your soundcard have an audio in? A cable from the cassette deck to the soundcard "in" should take care of the first 50%.. next is some software that will "record" the input into a computer readable format. Win 9x had an audio recorder feature that would record input sounds as a .wav file
If I recall correctly, your'e a linux guy too, maybe this will take you the other 50% of the way:
http://audacity.sourceforge.net/about/
