A good place to start is the KITP, for example their Blackboard Lunches.
The audio formats they offer are realaudio and ipod. As I do not own one of these white gadgets, I have to use the other option. My car radio can play mp3's (from its USB port or CDs). So I have to convert the .rm files to mp3. Here is how you can do that (so you don't have to spend as much time on it as I did):
In case it is not done already, install mplayer.
When you call it like
mplayer -quiet -vo null -vc dummy -af volume=0,resample=44100:0:1 -ao pcm:waveheader http://online.itp.ucsb.edu/download/bblunch/dine.rm
it will create a file audiodump.wav which in turn you can convert to an mp3 with bladeenc.
After you've done that for a couple of talks, use
mp3burn *mp3to write the seminars to a CD and you can hit the road, Jack!
Update: Of course you don't use mp3burn as that would produce an ordinary audio CD with maximally 72 Minutes playing time. You want a data disk with the mp3's on it so you really use a program like xroastcd.