Actually, this transfer is very easily done...
1) Drop by your local $1 store and pick up a "dual RCA plug(s) to mini-
phone plug" adapter cable...!
2) Connect the two RCA plugs with the "Line Out" jacks of the
cassette deck...then...
3) Plug the mini-phone plug into the "Line In" jack on your computer
sound card!
You can now save the cassette's audio content on your computer...
the formats depend on which audio applications are installed on
your computer...! You can also find and download applications
which allow a fairly complete set of sound-file format conversion
and/or storage...!