Apple have set up iTunesU with Stanford being one of the forerunners to use it.
To access audio that has been made available through iTunesU, iTunes must be installed on your computer. You use it to access audio files from lectures, conversations or whatever has been put on there. The idea is that any university can set a page up, and upload audio files to it.
Visit Burks on Learning and look at the links in turn to follow an interesting debate on the value of using this, rather than other methods of giving access to your materials.