Yes, you can do this.
You can transfer a rented movie to your iPad or to your iPhone from your PC/Mac when you sync your iPad or iPhone uing iTunes.
--You can choose to transfer the rented movie from your computer to the iPad or iPhone.
--The movie will be moved to your iDevice and removed from your PC/Mac.
You cannot move a movie rented using your iPad, IPhone, or iTV from that device to another device. But if you rented it with iTunes on your Mac or PC, you can transfer it to an iPad or iPhone.
NOTE: I have had problems with movie rentals disappearing from my iPhone if I transfer more than one at a time. It has happened more than once: about a day after I ransfer the films, all but the last one transferred disappear from the phone.