The output on the iPod and other MP3 devices isn't powerful enough on to power speakers by itself but that won't be a problem when you're done with this DIY ruggedised MP3 amplifier.
Instructables user Joe needed some extra juice for his iPod's output and some portable speakers to boot. He combined an amp and speaker setup in an Army surplus box with padding and a protective metal screen over the speaker to create a portable and rugged build. If you're curious why he went mono instead of stereo, he only had one spare speaker in his workshop to try out the build; you can easily build it with two speakers instead.
Check out the full build at the link below, even if you don't have an Army surplus box (or don't want to use one) you can adapt the build for any small case.