possible answer
I'm having the same problem. Is there a way to fix it? They showed up fine on my iPod video. Ughh, frustrating. First real problem I've had though.
If you're downloading the podcast separate from the iTunes store - then the association required in the ID3 tags may be missing.
Leo Laporte from episode 389 of the 'Tech Guy' podcast recently answered this question this way:
Q
Matt from Tenessee - Older podcasts don’t show up as podcasts.
Change the genre of the podcasts to Podcast. You can also try going into the iTunes directory and moving the podcasts into the iTunes Podcast directory.
Apple uses the extended MP3 tags available in ID3, that has the words iTunesPODCAST in it, and then iTunes see’s that and automatically puts it in the iTunes podcast directory. Leo recommends
MP3Tag
Show notes
here
Podcast
here