Hello there DOrtiz69,
Here are the instructions on how to move a rental to the AppleTV that was rented on a computer. They are from an article named How to rent a movie from the iTunes Store on your computer found here http://support.apple.com/kb/HT1390.
Once the rental is downloaded, you can watch it on your computer or transfer the rental to a supported iPod, iPhone, iPad, or Apple TV (1st generation):
- Connect the device and select it in iTunes.
- Click the Movies button.
- Select the movie, and then click Move.
- After all movies have been moved, click Apply in the lower-right corner of iTunes.
You must be connected to the Internet to transfer a rented movie.