There's no such thing as a root password on OS X, you can temporarily have root privileges but a root password doesn't exist. Are you talking about an Admin password? Most likely, you can reset that if you have the original discs that came with your computer, boot up with the first restore disc in the computer and hold down the letter C, this will start from the cd, when a screen pops up, go to the top menu choose Utilities > Password Reset Utility. This is where you can reset your password. A keychain is something that holds all your passwords stored on your machine, this may need to be reset but I don't know how that would affect your iTunes.