Again you have a choice of resources...
The steps are very similar to setting up a blog...
...except that you have to record or upload an audio file.
You can record directly into Podomatic or Swtichpod
using a mike attached to your computer.
If you want to record your sound first using a sound recorder, make sure to compress the sound file to MP3.
You can do this by downloading a free program called Audacity and
the LAME MP3 encoder. (Here is some useful information on how to configure Audacity and create an MP3 file for your podcast.)
Podomatic and Swtchpod allow you to upload your file to their site. (Here is a step-by-step guide on creating a podomatic podcast.)
Odeo, however, requires that the file is already on a web site.
This is how your finished podcast will look on Podomatic.
... which you can now embed on your blog.
The players look slightly different, but the result is the same.
Here's mine using Odeo on the We are the best blog.