Audacity is an open source audio editing software. It is available for free download for both the PC and the Mac Operating Systems. You can embed voice and music in multiple soundtracks. Once you export an Audacity file as an MP3 file, you have created a Podcast.
Click here for the link to download Audacity.
And to get the encoder that you need to turn it into an MP3, visit this part of sourceforge LAME Encoder
And, if you need help using Audacity, here is a quick reference manual
Audacity Video Tutorials - Click on this link to find simple tutorials on how to use Audacity to create podcasts:

Links to Royalty Free Music for Embedding in Podcasts

Here is where you can get copyright free music
And for royalty free sound loops, try Flashkit

Creative Commons Licensing

Here is a link to Creative Commons which "provides free tools that let authors, scientists, artists, and educators easily mark their creative work with the freedoms they want it to carry."

Here's our Something MP3 file:

This is a sample MP3 file demonstrating Audacity: