So you are saying that this is a limitation of the free version of Openkapow. Even without adding custom metatags to the free version, could the OpenKapow team at least add the < guid > metatag so as to support Podcast generation?

Looking at the source code of several podcast feeds, the URL of the attachement seems to be inside the < guid > metatag. I guess that there should be some open specs about this somewhere. A podcast with support of itunes also has many specific meta tags like < itunes:author >, < itunes:keywords >, etc. but I don't use these ...