Hmm... Try this :
Start > Run > Gpedit.msc {Press Enter}
In MMC, browse to :
Computer Configuration > Windows Settings > Software Restriction Policies
Click on Additional Rules
In the Right Hand pane, Right Click and select New Path Rule
Enter the path to the executable you wanna disable (say c:\program files\powertools\powertools.exe ) and Security Level to Disallowed. Click on Apply , OK.
Now to prevent this setting to affect administrators do this :
Click on the Up One Level button on the toolbar.
Double click on Enforcement.
Select the option that says: All users except local administrators.
Click on Apply, OK.
You will need to log off and on to have the changes in effect (atleast I needed to ).
Phew ..