c:\Documents and Settings\Administrator\Application Data\Apple Computer\Safari\Preferences.plist
And add inside this file new entry:
Than save it.
Close all your Safari browsers and open it again.
You will see in the menu new menu entry called Debug.
If the above mentioned does not work for you, try the following:
Locate the Safari.exe file and run it using command Safari.exe /enableInternalDebugMenu.
(default location for Windows 7 is C:\Program Files (x86)\Safari)