I think, the BIGGEST difficulty is getting Gnome2 to Aqua look, for getting GTK-Apps looking like qt-apps. It's really ugly, if the themes for gtk and qt aren't equal (--> buttons, dropdown,etc...)
Only way i see to do this is installing Gnome1.4, there are several really good aqua GTK-themes, which then will be shown under kde, too...
Second, the transparent widget isn't possible by now, as the magnifying icons in the panel...