I had an installation of Umbraco that didn't show all of the icons in the editor.  Every node clicked only showed save, publish, undo, and the style dropdown.  Here is what I did to make them appear: (4.0.2.1 and IE 6).  Go to Tools > Internet Options and set the temporary internet browsing history to "Automatic"  and bump the space up to at least 50mb.  That fixed our issue, and the icons appeared.

Kuda