Sync priority problem

You can't. By design, the iphone will sync itunes content with ONE computer at a time. Any attempt to sync such content with a second computer will result in ALL itunes content being first erased from your phone and then replaced with the content from the second computer. This is a design feature of the iphone & cannot be overridden. Because you formatted your drive, your phone sees this as a "new" computer. You need to authorize your new computer, Store>Authorize this Computer. After that, you can transfer purchased content, File>Transfer Purchases. Music you ripped on your own, playlists, photos, etc., will have to be extracted from your phone BEFORE you sync or do anything else. Apple makes no provision to do this as its expected that you will maintain a backup. The music & photo sync is one way, computer>phone. You'll have to use third party software, here's one good example:

http://www.wideanglesoftware.com/touchcopy/index.php