Firstly, you need something to play the cassettes on. Ideally you should use a 'hi-fi separates' tape deck, with RCA ("phono") sockets on the back of it but (as long as you keep the volume setting low) it's possible to use a 'Walkman' type cassette player.
Then you'll need a cable to connect that device to the input jack on the back of your computer. (You can't send the signal directly to your iPod). If you're using a proper cassette deck you'll need something like this:
http://www.maplin.co....e.aspx?ModuleNo=31700
For a Walkman you'll want this:
http://www.maplin.co....e.aspx?ModuleNo=11422
(NB: Much as I love Maplin's, they can be very expensive for leads like those. Try 'pound shops' and 'discount stores' for far lower prices).
Then you'll need some software. This is what nearly everyone uses:
http://audacity.sourceforge.net/
In its native form, that programme can't export files into MP3 format. (It's a licensing issue). You'll also need this to fix that problem:
http://audacity.sourc...install&item=lame-mp3
I also strongly recommend reading the documentation! (Audacity is fairly intuitive but it still helps to read the instructions!):
01:43 Tue 04th Jan 2011