Where does iTunes store the Podcast subscription info and preferences?
They're in the iTunes .plist-file on a Mac.
Since you don't specify platform, I can't offer that much. In Windows, they're almost certainly stored in a similar preference file. In Mac OS X, they're not conveniently readable.

If you just want to back up your subscription info, locating and backing up the iTunes preferences will do it. If you need to scrape/publish the subscription info, that's beyond my capabilities. Hope this at least gives you a jumping-off point.