I haven't used Front Row much...it seems as though it is reading your Movies folder and your iTunes library. Try removing one video podcast from iTunes and see if it is then removed from Front Row.
If this is a strict requirement of yours you may have to look at some of the other media center apps. There are a few in various stages of maturity. I also have an Apple Script that will launch DVD Player feeding it a VIDEO_TS folder. You can get DVD Jacket covers as icons and attach the script to each DVD Jacket and just use Finder for an interface. PM me if you are interested.
All of these alternatives are probably going to take more time than simply skipping past the content you don't want to view while in Front Row. Or better yet, create a smart playlist in iTunes that only gets the content you want "where genre not podcast", etc.