I have both Apple TV and an iPhone and need advice on what format and size to put my video into which will work on both devices. I don't want two copies of every movie.

My previous movies which worked well on Apple TV (by exporting them in Quicktime Pro) sadly won't work on the iPhone. By exporting for iPhone, the quality is really low on Apple TV. Can anyone please advise?

Because of the screen resoulution difference, you wont be able to have a video playable on an iPhone that will look good on your TV. Either convert the movie and save it to a disk, or save both files on your Hard Drive. Good thing is the iPhone movies should be small in size.