I'm watching these iphone tutorials on iTunes, and for some reason I can only stream the videos.
is there a way to download them so I can enlarge the screen?
Press the "FREE" button that normally displays the price of the item to download the item into your library under the "iTunes U" heading. Alternatively, press either the "Subscribe Free" or "Get All" button to add all episodes to your library.
Once you've done this, playing the file from your library will respect the settings under Preferences → Playback → "Play Movies and TV Shows:"