Between work, home, and the family network, not everyone spends time on just one computer these days. So Apple lets you play copy-protected Store purchases on up to five computers: Macs, PCs, or any combination. You just need to transfer the files and then type in your Apple user name and password on each computer to authorize it to play any songs, videos, or audio books purchased with that account. Each computer must have an Internet connection to relay the information back to Store headquarters. (And don't worry—you don't have to authorize each and every purchase; you authorize the computer once to play all the items bought from an account.)
You authorized your first machine when you initially signed up for an Apple Account. To authorize another computer:
❶ On the computer you used to purchase an iTunes Store item, grab any file you've bought from iTunes. You can drag the files right out of your iTunes window onto your desktop. You can also find all the song and video files in your iTunes Music folder: My Documents→My Music→iTunes→iTunes Music (Home→Music→iTunes→iTunes Music). Store files are easily recognizable by their .m4p or .m4v file extensions. Movies are stored in a folder called Movies; TV shows are stored in folders named after the show.
❷ Move the file to the second computer. Copy the file onto a CD or USB drive, email it to yourself, transfer it across the network, or use whatever method you prefer for schlepping files between ...