I don't know if it works on Windows 8 or not but it works on Windows Vista/7 very well. Press the Win+U key which will open the Ease of access center or you can open it through Control Panel as well.
Now click on the option Use the computer without a display
and another window will popup
And unchecked the option Turn on Narrator
and click Apply button to apply this settings. Now when you press the Win+Enter narrator won't be start.