If I download (Rent) a movie from itunes on a PC but If I wanna watch it on an iPad will I have to download the movie seperately again on the device I wannna watch in this case the iPad ?
I don't think there is any way to transfer an apple movie file from iTunes to the iPad - I might be wrong perhaps someone else here knows if it is possible
Probably your best best option is to download the lower res version if the connection is slow