The previous reply is not wrong, but that's been possible since before iTunes 7. What iTunes 7 added is a feature to "Transfer Purchased Music". You must have the iTunes account activated on both machines. Then when you do have the iPod set for automatic synchronization, plug the device into one system, sync it up, and disconnect it. Plug it into the second computer and you should see a message that asks you what you want to do. One of the buttons says "Transfer Purchased Music". This will download anything you purchased from the iTunes Store into the Library on the second system. The purpose of this feature is that if you buy content on computer A, you can use the iPod (without using the hard drive and taking up 2x the file size) to transfer the content to computer B.