I just stumbled across this while listening to the de Young Museum Podcast:
When listening to an enchanced Podcast on iTunes (i.e. one that contains multiple photos and chapters), click on the Artwork preview pane to bring up a separate artwork window. You can now navigate the chapters by pressing the left or right arrow keys.
It's a convenient way to browse images in an enhanced Podcast.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060922150616779