set up the tape player and where you usually plug in the headphones plug in a cable that has a male jack on each side of the cable.
plug the other side into the microphone socket on your computer.
start up the sound recorder (start,all programs,accessories,entertainment,sound recorder)
you will have to ajust a few bits on it but it should be ok to start recording.(see the help file on it)
and then just save the file.
All the best