Require users to press Ctrl+Alt+Delete checkbox is grayed out

http://www.wincert.net/tips/microsoft-windows/windows-xp/2163-require-users-to-press-ctrlaltdelete-checkbox-is-grayed-out.html
Click Start | Settings | Control Panel | Administrative Tools | Local Security Policy
In the left pane browse to Security Settings | Local Policies | Security Options
In the right pane change the value for, "Interactive Logon: Do not require CTRL + ALT + DEL" from Disabled to Enabled