I have the Microsoft Wireless Optical Desktop Receiver 2.1 (Model 1028) with
Wireless MultiMedia Keyboard 1.1 and Wireless Optical Mouse 2000. In the
Device > Power Management settings of both the mouse and keyboard, although I
can uncheck the 'Allow this device to wake the computer' option, they can
still bring my system out of Sleep mode.

Also in the same Properties, the option 'Allow the computer to turn off this
device to save power' isn't selected and is greyed out, which (in the case of
the mouse) I'm sure is connected with the fact that the mouse's optical light
remains on after shutting down and switching off at the mains.