It's not as dirty as it sounds. A "fisking" on Andrew's site is when he takes the text of an article and speech and intercuts it with his opinion of pointing out how they are twisting words to their advantage. As such, a podfisk, is that same practice done in audio/podcast form.

It is available here, and worth a listen:

http://time.blogs.com/daily_dish/2006/06/podfisking.html