iTunes questions

Hi, i've been purchasing the tv programs from itunes recently, and i just wanted to know, if i format my hard drive or buy a different macbook/pro, will i lose all my tv programs.

Can i just copy them to my external hard drive and then copy them to my new itunes on my new laptop?.

I just dont want to spend a lot of money of these tv programs, then i lose them all when i reinstall osx or something.

Thanks

How do i unregister a computer?.