System32\msgina.dll
I think this fie is the one you are looking for. It has a couple of "locked computer" dialogs along with the classic logon screen etc.
Using reshacker, they are dialog 1400, 1500 and 1900 on my laptop (Windows XP SP2 English).
Hope this helps in some way.
[offtopic]
On a side note, a look at dialog 2210 (Shutdown event tracker) shows the people at MS have a slight sense of humour
[/offtopic]