In general iTunes doesn't make backups. That is up to the end user, and they will be where you put them. If you mean iOS device backups these are stored in C:\Users\<User>\AppData\Roaming\Apple Computer\MobileSync\Backup for Windows 7. There is one rolling backup per device, unless you're used a backup to restore in which case that backup is put to one side and could be used again. What are you trying to do?