Have you already planned which cassette deck and sound card to use?
If you have a *large library* of tapes to convert, you better go with very good equipment. (Good cassette deck = Minimized wow & flutter, best sound quality, etc. Good soundcard = Low computer noise, good preamps, etc.)
The only good cassette decks are made by Nakamichi(You might think you have a good one until you hear a Nak), but they stopped producing them so you need to get a used unit that will probably need service. (Suscribe to naktalk mailing list if you think you're going to use one instead. A Nakamichi Dragon will calibrate itself automatically to match each tapes even if they were recorded on different, probably never serviced, machines)
As for the digital format, at least save your "original recording" to a lossless format before converting to MP3. In a few years MP3 will probably turn obsolete because of it's low sound quality.
Apart from that, you need a good sound card(M-Audio, Auzentech, Audiotrak),
editing software (A deck is saving you time here, there are less "corrections" to bring. If you get a new card, there's probably going to be some with it, but what else, you can use Audacity, it's free)
cables. (Monster Cable isn't necessary and never will be. It's marketing BS. The best is to build cables, but a pair of 3' RadioShack Gold Series RCA cables will do the job.)
Then, time is needed. (To separate the tracks, etc.)
There's some sound enhancing software, but use only if the original tape sounded bad.
More info could help to see if you really need an high-end deck and sound card.
Edit:
there are 10 kinds of people in this world... those who understand binary and those who don't
LOL