You could play the cassettes on a tape deck that has a headphone output plug, and use a 1/8 inch to 1/8 cable to connect the headphone out to the microphone input on your computer, get a recording program(audacity is free simple and good quality
http://audacity.sourceforge.net/ if you don't already have one) press record in audacity, then play on the tape deck. This isn't really ripping as much as it is dubbing, but I can't really think of any other way. I've done this to make CD of a vinyl record before and it does well, although it's obviously slower than ripping.
I hope I helped.