Prepare to Sync
The first step in syncing is to send all your information from one Mac (preferably the one with the most data) up to your .Mac account on Apple's servers. Once it's there, you can synchronize your other Macs to it. If you don't yet have a .Mac account, you can get one in this first step.
Open the .Mac preferences: From the Apple menu, choose “System Preferences…,” then click the “.Mac” icon.
In the pane that appears, click the “Account” tab. If you don't have a .Mac account yet, this pane will ask if you want to sign up for one. You must have a .Mac account to sync Macs. If you want to switch to another .Mac account, change ...