Change the iPhone/iPod backup to another drive in windows OS

1. Move the “Backup” folder from the “C:UsersAppDataRoamingApple ComputerMobileSync” location and place to an external drive, let’s say to “D:itunes”.

2. Open command prompt from Start –> Run and type –
mklink /J “C:UsersAppDataRoamingApple ComputerMobileSyncBackup” “D:itunesBackup”

after successfully done, u will get a msg –
Junction created for C:UsersAppDataRoamingApple ComputerMobile
SyncBackup <<===>> D:itunesBackup”
and will create a shortcut folder “Backup” under “C:UsersAppDataRoamingApple ComputerMobileSync” 
Have fun!!! now you can have GBs of backup in external drive with out affecting to the OS installed drive.