If the stuff is all mixed and all you want to do is get it onto the computer (i.e. you won't need more than the most basic editing functions), try Cakewalk's Pyro. $49.99, it'll record from the line in on your soundcard and allow you to make .mp3s and burn CDs.
Get the mix right on your tape machine, take the left/right outs off the tape machine to an adaptor that'll fit your soundcard (usually a 3.5mm stereo miniplug). Call up Pyro, hit record, then hit play on the tape. You can then do some basic editing to get the start/stop times right and mormalize the levels.
Hope this helps.