How can I authorise my brothers account with my MacBook Pro?
It's because I wish to download a film on his computer, which I originally purchased on my computer...
iTunes-OTHER, OS X Mountain Lion (10.8.2)
You can authorise an account via the Store drop-down menu at the top of iTunes e.g.
But re-downloading an account's past purchases on a computer will potentially tie a computer to that account for 90 days : http://support.apple.com/kb/HT4627