when using an extenal HD to import to itunes why do the file copy to my MBP HD

Hi Guys

I am very new to the MAC world and would like a little help please.

when using an extenal HD to import to itunes why do the files copy to my MBP HD, i thought itunes just located the files.

I have a 1TB external HD but only 500GB internal and when i import my flims so I can use Apple TV, i get a pop up saying can not import all files hard disc is full. I dont want the files on my MBP HD. how do i set up itunes using multiple external HD.

Any help at this early stage would be appreciated, thanks in advance.

Darren

exter