Q: purchased and downloaded tv episodes only play 30 seconds

Hello dhillapple,

I think I would start here with this article named Troubleshooting iTunes for Windows Vista or Windows 7 video playback performance issues found http://support.apple.com/kb/ts1718.

If that troubleshooting doesn't resolve the issue, then I would suggest creating a new iTunes library with this iTunes: How to open an alternate iTunes Library file or create a new one http://support.apple.com/kb/ht1589 and then downloading a few of the videos with this Downloading past purchases from the App Store, iBookstore, and iTunes Store http://support.apple.com/kb/ht2519 to it to see if the issue persists.

If the issue does not persists in the new library then I recommend recreating your iTunes library.

iTunes: How to re-create your iTunes library and playlists

http://support.apple.com/kb/HT1451

If the issue does persist in the new library then I would use this article to help isolate whether or not it is system wide or user specific.

Isolating an issue by using another user account

http://support.apple.com/kb/TS4053

All the best,

Sterling