You can use Backup and restore, though there are many easier solutions.
1. Assuming that they are all on the same network, copy the files over the network using Windows Explorer
2. If they are on different networks, you can use Live Sync to keep the folder of Music synchronized -
http://sync.live.com 3. Copy the files to an external disc from one PC and then attach the disc to the other two PCs and copy the files from the external disk.
-steve
Microsoft MVP Windows Live / Windows Live OneCare & Live Mesh Forum Moderator