I recently purchased an interesting product called PlusDeck2 which is essentially cassette deck that you install in the PC, connect to the sound card and COM port. It comes with software that automates conversion process by controlling deck via the COM port and digitizing tape output using existing sound card.
Who needs to convert tapes? Well, I do :-). For example, my daughter loves to listen to Russian fairly tales and many of them are only available on tapes. However, my Prius does not have tape deck so I really need a CD, preferably MP3 or WMA so I can fit tons of stories on a single disk and keep her entertained (and myself not bored listening to the same story over and over again). My daughter also likes to listen to stories and music at home and we don't have tape deck there either. All audio titles are sitting either on CDs or on my music machine.
PlusDeck is a good piece of hardware, I installed the deck in 5 minutes and after tinkering for about 20 minutes with the sound recording levels was able to begin conversion. The software lacks recording level meter so usually you end up oveloading the sound card. I ended up keeping line input level at about 10-20%. The other issue is that you probably want to get at least simple sound editor to get rid of tape noise and trim recorded file into separate titles. The accompanying software seems to be capable of splitting recording into separate songs or parts, but some reviews mentioned that it was not very precise so I decided to record each side into a separate WAV file and then split it into pieces myself. Manual suffers from poor translation but you probably only need to look at the connection diagrams, everything else is pretty much self explanatory.
Sure, if you already own a tape deck, you can simply connect it to the sound card and use your favorite recording software. But it you don't own one and/or like the automatic process, PlusDeck will help. It also can convert tape directly to MP3.