This is really one of those wonderful tools that does one job very well -- in this case, preparing an XML file for posting a podcast for iTunes. It's simple to use. The developer's web site offers a Flash tutorial on how to use it (only takes a few minutes to view it, but it's pretty thorough). This is available for Windows or Mac.
Podcast RSS Buddy allows you to prepare a .xml file that contains the info that iTunes needs: Name of podcast, name of each episode, author, time, length of podcast, etc. You can even edit info for past podcasts or delete them entirely.
When you download it, you get 5 demos. In my case, that was enough to convince me that it was the tool we needed.
Bear in mind, to post a podcast to iTunes, you must first register with iTunes. But it's an easy process. Our podcast was approved in less than 24 hours.