There are lots of podcasts hosted here, as you can see from surfing the podcast tag in the sidebar of this thread.
You can set it up this way for free by:
(1) finding an external host for your mp3 files that allows hotlinking, like Fileden. Then use that link in the blog to provide a download and also to use for the Audio Player below
(2) use the WP Audio Player http://en.support.wordpress.com/audio/
(3) just write up your notes and put them all in the post with the above
You can do this more easily if expensively by purchasing the Space Upgrade; then you can host the files right here at WordPress.com and upload them just like you would a picture.