I've transferred quite a few tapes successfully to the PC, then to cd using a little program called Polderbits.
It's the one and only piece of shareware that I've eventually paid for, as it was so useful, and above all, simple to use.
For converting to mp3, wav etc I use dBpowerAmp, a brilliant little free piece of software.
There are hundreds out there, though- it's worth test-driving a few to find what you're comfortable with.
Judging by some of the tape deterioration I've come across, it's well worth the time invested too.