The way I do it is through my old DCC deck. It's a dinosaur, but it's a good converter. DCCs play both analog and digital cassettes and have digital coaxial and optical outputs. Some DCC decks will play an analog cassette and send a digital out directly, and some won't--mine doesn't, it's a cheapy, so what I do is run my standard cassette deck into my mixer and run my mixer's output to the DCC deck. (or you can actually bypass the mixer and just go deck to deck) Then I put an old DCC cassette in the deck and put it in record mode, paused. This converts the signal coming in to the DCC deck and sends it to the digital outs, and I run this (digital coaxial) into my sound card. Then I just record the tape in soundforge as a wav--ready for conversion.
Perhaps not the most elegant solution, but it works great. In fact I use the configuration globally to convert my old Peavey mixer into digital. Of course any nice DAT deck would work also.
DCC decks are getting harder and harder to find, but they go cheap, and I just scared
one up on eBay.
eBay item 5735687136 (Ends Dec-04-04 18:00:00 PST) - Phillips DCC-900 Digital --two days to go, no reserve, going for $1.00 (no bids) with $18 shipping from Denver.