Technically, you can flip-flop systems, but it's a P.I.T.A. to accomplish since the software will have to re-format the device each time. And of course when it reformats, you lose all of the info you've stored on the device and have to hope that it's available for you to reload!

Most of the time, it's much easier to stick with one format. If you're really serious about using the MacBook as much as it sounds like you'll be for school stuff, you may want to wait until you have that before you put very much on the iPod.

Good luck!