Music is not part of the backup at all. If you purchased it from the iTunes store, you can re-download it. If it came from another source, then you will have to re-sync it from your computer. If your computer will not run a version of iTunes compatible with iOS 6, then you may have to consider getting a newer computer.
As for the photos, the camera roll should be part of the backup. Photos in albums synced to the phone from a computer are not part of the backup.