Thank you for your response.
This addresses one issue that the images are using full relative paths rather than using parent paths, but I would prefer to control the urls so that they are absolute rather than relative.
I have implemented your example with the additions below. Please let me know of other ways to change the rendering of the urls.
protected void RadMenu1_PreRender( object sender, EventArgs e )
foreach ( RadMenuItem itm in RadMenu1.GetAllItems() )
itm.ImageUrl = itm.ResolveUrl( itm.ImageUrl );
itm.ImageOverUrl = itm.ResolveUrl( itm.ImageOverUrl );
itm.ImageClickedUrl = itm.ResolveUrl( itm.ImageClickedUrl );
itm.NavigateUrl = itm.ResolveUrl( itm.NavigateUrl );