http://rackerhacker.com/2008/11/02/syncing-an-iphone-with-a-new-mac-without-hassles/

Make sure that iTunes is not running on both Macs. Disconnect your iPhone/iPod from both Macs. Copy your iTunes folder. /Users/username/Music/iTunes Copy your iPhone/iPod backups. /Users/username/Library/Application Support/MobileSync Copy your iTunes configuration files. /Users/username/Library/Preferences/com.apple.iTunes* Open iTunes on your new Mac and verify that Applications and Ringtones appear. Connect your iPhone/iPod to the new Mac and accept any new authorizations. Use iTunes on your old Mac to de-authorize the computer.