Leisure Units Music Technical Assistance, Please

A long time ago I retrieved all the master tapes of the Leisure Units music from Skyline Studios. I think they may have been about to throw them out, in any case, I gave them to Aly years later. I had cassettes made of their songs and I’d like to digitize them and make MP3s for myself and anyone else who would like them. But two things: I don’t know how and maybe someone has already done this?

If you have could you let me know?  Or, could someone else help me figure out how to do this? All I have to play them is a Sony Professional Walkman, so I need to connect the Walkman to my Powerbook and I guess I could use GarageBand to record them while they play.  Except I don’t know what cable to buy to plug from which output in the Walkman to which input in the Powerbook. I’m sure I could figure this all out, but I thought maybe someone out there would just know.  Or again, someone else may have already done this!

Thank you in advance for any help anyone can give me.  (This is Aly, Jeff Zaleski and me at lunch, last year I believe, in the summer.)