I'm not sure if you've been made aware of this resource, I've done a quick search on the forum but couldn't find reference to this so hopefully it's new.
Berkeley University offer free webcasts of their
"Introduction to General Astronomy"
course. The site offers the user the ability to download an MP3 of the webcast or the option to view the webcast via RealPlayer (anyone know how you can save and view these files offline?).
Don't be put off by the first webcast there was a microphone problem the other webcasts seem to be perfect and if you've got a fast broadband connection I'd recommend the video webcast. In total there are 41 lectures available which seem to be about an hour long.