Record the tapes onto the computer. Then you can either straight out record them to CD, or there are many software packages that make them sound more listener-friendly. I use Steinberg's Clean software when doing something like this, and it works good for me. There might be better ones, but Clean works good to get some of that cassette hiss out, and to bring some liveliness back to the sound. You need a CD burner in the computer obviously. I've seen Goldwave recommended as a good free audio recording program. You need to plug your cassette deck's line out into the soundcard's line in (not mic in). Then record using Goldwave, or whatever other software you are using. You save the recordings as WAV files. Then you can do that "sweetening" using Clean or something similar. Then you burn the WAV files to a CD. Presto chango! You now have a possibly better sounding CD from that old cassette.
Jake