There's a new feature in Apple's iTunes 9 music software called Home Sharing that lets all the computers in your home easily transfer media back and forth. It's a great solution for those times when you buy an album or TV show on your computer, and your wife or child wants a copy on their computer as well.
The first step is to make sure all the computers in your home are running iTunes 9 or later and are connected to the web through your local wired or wireless router. Next, find the first computer you want to share from and select the Home Sharing icon in the left window of iTunes.
In the main window, you should see a place to plug in your iTunes store log-in and password.
After hitting Done, repeat these same steps on the other computers in your home. iTunes only allows a maximum of five computers to be authorized, so if you're managing more than that, choose carefully.
After you're done, you should see each of the other libraries appear in the left window of iTunes. From here, you can browse and play selections, and best of all, transfer content out of one library and into another.
Use the settings button in the lower right corner to automatically transfer any new iTunes store purchases between libraries. Automatic syncing only applies to purchases made after the setting is switched on, so old purchases will need to be transferred manually.
To see a video version of this tutorial, head over to CNET TV.