Click "Start / Run" and type "gpedit.msc". It should open a windows like the one below
(Click on it to open a bigger image).
In that go to the branch on the left hand side frame following the below path
"Local Computer Policy / Computer Configuration / Administrative Templates / System"
Clicking on "System" will list lots of items on the right window. One of them is "Turn Off Autoplay".
Double click on that, make sure to select "Enabled" radio button and on the list box below, select "All Drives".
This should disable Autorun in all usb and cd/dvd drives on the system.