Well, if you tried via the registry already and it didn't work, try group policy
Start>Run Gpedit.msc Go to user conf>admin templates>system >windows components>explorer
Under Remove the folder op, choose the enable, applly, go back and change to disable. Maybe toogleing off then on will do the trick...
And here is a regfix:
Download number 129 from here and run it:http://www.kellys-korner-xp.com/xp_tweaks.htm