Apple has it's method, others has their own way. You have to ask the service you used to buy the music on how to move.
Bob
I have 2 laptops both on a network and i want to transfer all my protected music onto 1 of the laptops but when i do that it says the liscence for this piece of music is on another computer!!! i dunno what to do because i have literally hundreds of pounds worth of proected music and i cant listen to it on my new laptop which is the latest sony vaio

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic