To change the user password in Leopard(10.5.x) or SnowLeopard (10.6.x)
- Hold "Command + S" key on your mac keyboard to boot your mac into single user mode.
- Execute command "mount -uw /" in shell.
- Run below command "launchctl load /System/Library/LaunchDaemons/com.apple.DirectoryServices.plist"
- Execute command : passwd
- change the password of root.