This Apple doc provides the location of your iPhone backup -> iTunes: About iOS backups
The folder where your backup data are stored varies depending on the computer's operating system. Make sure the backup folder is included in your periodic data-backup routine.
iTunes places the backup files in the following places:
- Mac: ~/Library/Application Support/MobileSync/Backup/
- Windows XP: \Documents and Settings\(username)\Application Data\Apple Computer\MobileSync\Backup\
Note: To quickly access the Application Data folder, click Start, and choose Run. Type %appdata% and click OK.
- Windows Vista and Windows 7: \Users\(username)\AppData\Roaming\Apple Computer\MobileSync\Backup\
Note: To quickly access the AppData folder, click Start. In the search bar, type %appdata% and press the Return key.
For more info about moving your music to the new computer, see this -> iTunes: How to move your music to a new computer
Also, you'll have to move your photos over manually, iTunes has to do the one-way street syncing of potentially coyprighted data. It does allow you to transfer iTunes Store purchases that haven't been moved to your new computer though.