A rented movie can only be stored on one device. In the normal course of events when you put a rented movie on a device the original is removed from the library. No real surprise if iTunes won't copy it via home sharing. You could move the file manually, remove from the first library and add to the second. It should work and not compromise the rental period, but don't blame me if things don't work out.
i set up home sharing and everything in the library seemed to come over except the rented itunes movie I was trying to get
You cannot copy rentals using Home Sharing. Also, you cannot transfer rentals between computers.
Also see this -> http://support.apple.com/kb/HT1657
If you download a rented movie on your computer:
- You can transfer it to a device such as your Apple TV (1st generation), iPhone, iPad, or iPod if it’s a standard-definition film (movies in HD can only be watched on your computer, iPad, iPhone 4 or later, iPod touch (4th generation or later), or Apple TV). Once you move the movie from your computer to a device, the movie will disappear from your computer's iTunes library. You can move the movie between devices as many times as you wish during the rental period, but the movie can only exist on one device at a time.
If you download a rented movie on your iPhone 4 or later, iPad, iPod touch (4th generation or later), or Apple TV:
- It is not transferable to any other device or computer."