I’ve done the change
In fact, it is the authui.dll that effects, its location is X:WindowsSystem32authui.dll
you can remove it with a early version, which makes you can change the background of the logon screen with some tools, such as Vistamaster, which is a Chinese tool to modify Vista and WS2008.
here is the dll file
[attachment=0:34acjvl7]authui.rar[/attachment:34acjvl7]