Let the aggregator retrieve the podcast audio

Let the Podcast aggregator update (in Doppler: push "Retrieve Now"): your MP3 file should download

Enter the RSS feed in your podcast aggregator

(here in Doppler)
Enter the feed URL in your podcast aggregator
(typically it will then get the podcast name)

Validate your feed

Verify your feed on feedvalidator.org (just to be sure - the result should be "This is a valid RSS feed").

Enable SmartCast feature

Click on the SmartCast option

Create the Feedburner feed

At www.feedburner.com, burn your http://[your_podcast].blogpost.com/atom.xml Atom feed.

Publish and check link

Publish the post, and check the blog (the title of your post will be clickable and point to the MP3 file)

Create new blog post with MP3 URL

Click on "Posting"/"Create"
Create a new Post, and put the MP3 file you want to podcast in the 'Link' field.