I'm not going to bore you with the details, but in hopes to help others to avoid the same trial-and-error process I went through, I put together a sample podcast feed in which the tags' contents are the names of the tags themselves.
If you subscribe to the feed [link only works if you have iTunes installed], you'll quickly see what I mean. Click around the iTunes U.I. and the podcast and episode properties and you can learn how each tag is displayed. Also, sync it to your iPod and you can see how the tags are displayed in the iPod U.I.
Unfortunately, my sample podcast does not validate with feedvalidator.org. The reason is simple, though: it doesn't like the tags' contents being the tag names themselves. For example, the