benzwu

in OS X: ~(your home directoy)/Library/Application Support/MobileSync/Backup/ in Windows XP: C:\Documents and Settings\user\Application Data\Apple Computer\MobileSync\Backup in Windows Vista, Windows 7: C:\Users\user\AppData\Roaming\Apple Computer\MobileSync\Backup

If you direct download the ipsw file, just put it under -> your home directory -> Library -> iTunes -> iPad Software Updates For iPhone and iPod, I believe put to the similar named folder too. Note: if you can’t find the software update folder, just create one.