It is essentially the same process as going from vinyl.
the method I use (described in that thread) is to run the analog source into your sound card's line in, and record it to a WAV file. from there you can burn it to cd or encode it mp3 or whatever. This will take some setup, but it is cheap.
there are also some combo cassette deck/ cd burner combos. these are more like audio components.. might be pricy but this would be the easiest way to go.
Do you have mic or sound inputs to your sound card? If so, you should be able to run audio left/right out from the cassette deck to inputs on the sound card. It might require a y-cable (RCA-PIN females * 2) to run the cassette outs to a 1/8" male jack for the sound card.