I have always found it very difficult to tape lectures because you have to get your device so close to the lecturer and sound quality can vary if they move etc. Why don't you encourage your school to video tape lectures and then put them on the web for all of your classmates. That's what our school did, it was very handy being able to watch lectures from home.
Most PDas have recording software built in, a basic microcasette recorder might work too, you might have to switch tapes in the middle of the lecture depending on the length of the lecturer. An IPOD of course would work well, there is a addon you could buy for Ipods to record lecturers however a PDA would be more multifunctional.
Let us know what you decide on.