From ZuneInsider :

Please plan on downloading the new Zune Marketplace software on November 13th, then visit the main podcast section in the software to “Suggest a Podcast” for inclusion in the public Podcast Marketplace.

We also have a cool “Personal Podcast Feed Submission” feature in your podcast subscription collection area that is accessible after login inside of the new Zune Marketplace.  This personal feed submission feature will enable advanced podcast users to add a personal list of podcast feeds to their own subscription “Collection” area.  Each of those personal feeds submitted to your collection will not be seen by me or my team for general marketplace inclusion.  This will be your personal and private collection of podcasts that some may or may not be in the general marketplace podcast library.