What burning software do you have with your c\d burner. Nero, roxio?
If you have roxio then it should have a separate section called sound stream. This will convert and clean up slightly the sound from the tape.
To transfer the audio, you would need a jack plug and lead from the tape player to audio input into the back of the sound card. It just plugs in like a headphone socket. You do not have to open the case.
If you do not have roxio, then there are lots of free programmes on the web that should do the same.