Your biggest problem here could be the tape quality. You didn't say what type of machine it is playing back on. Double cassette, JVC, Sony etc. I'll assume that you have a red/white lineout jacks. I've done this before with a "y" line out cable ending in a mini 1/8 plug. Insert into your sound card line in and record to hard drive through your chosen software. Use cleanup plugins later for tape hiss.

First step though: clean your tape heads of old tape oxide with a q-tip and head cleaner or as some do, rubbing alcohol. Run a few songs and check the heads again to see if you have oxide coming off of the cassette tape. If its bad, you may have may to stop the recording process a couple of times for cleanup. But this will help the fidelity. Also, was the tape recorded using Dolby to this particular cassette player. If the player has a dolby on/off button you may have to determine if the tape sounds better with or without the dolby on.

Think that's about it, I think. Works fine.

Cheers

Ian
My "Original Tunes" Site
My gene pool needs more chlorine.