[Christien]

Considering you're going from cassette to digital, it doesn't really matter how good quality of a sound card you're using, because the cassette will easily be your weakest link. As for cleaning up tape noise, I use Cool Edit Pro (has since become Adobe Audition, which I had a quick look at and didn't bother with). Its built-in noise reduction feature (actually hiss reduction for tapes) is phenomenal once you get used to how it works and get the settings right. It's one of the best noise reducers I've ever used. It takes a while, and it helps if you read the manual to understand what the various parameters are, but it's well worth the 20 minutes or so it takes to figure it out.

You might be able to find a shareware version around somewhere - it used to be available with a 30-day lockout, IIRC, but I have no idea what's happened since Adobe bought them out. There are "found on the ground" copies out there...