holy crap thats a lot of tape lol

you will only be able to record in real-time if you want to keep it simple...

on the hardware side, you just need to plug the line out from your tape player into the line in/mic socket on the pc.
you may need to adjust the mic sensitivity in your operating system depending on how the signal comes through. you may need to buy a connector to convert the line-out from the tape deck into the smaller pin on the mic socket, available from electric/audio places.

then its a case of finding some software/freeware that can record live from your mic socket, and convert the recording into somthing convenient like mp3.

under windows theres any of hundreds of little apps that can do it, sureley there must be a simmilar thing for linux....all i can suggest on that front is searching for linux audio apps