I've been playing around with this:
http://forum.xda-developers.com/showthread.php?t=386451
It seems to be what you are asking for. In the settings I just checked the "lock on wake up" and it works without a password. The only issue I've found so far is that when you hit the power button to wake the device it flashes to the home screen for a second and THEN locks the device. So essentially you have to hit the power button twice to get to the unlock screen. Hope this helps.