By some independent tests it has been clarified that this method only works in Windows Vista and Windows 7. You will not see the icons on 2000/XP (I think the same for 98/ME). The way WinRAR is adding his icons to the context menu is more complicated and uses its own key and a DLL file, in which all the data about icons and context menus is stored.
Probably there is something in Vista/7's registry that allows them to read and understand the "Icon" key, if you know where it is, then we get it to work on 2000/XP. Otherwise, no support for them or I will have to learn how is that DLL composed.