XP explorer backgrounds do work as long as common tasks are showing,if not,nothing will happen.Have tried to skin common tasks as well ,now only need to skin background,see pic-
You need to go to Backgrounds-edit explorer background bitmaps,make sure active(or inactive) whichever you want is selected.Select arrow next to edit image for quick import of whatever file you want,should work hopefully(for images as windows backgrounds)
As you can see the controls are in XP specific-edit shell style bars and arrows,to skin common task area.
Pic used was Santa Fe Stucco in windows directory,SKS6 Also used.
Apologies to Night Train.

To change skin colours go to SKS6-change skin colours,in dropdown menu make sure show skin defined skin colours are showing,then select window background and change the colour.(for colours as windows backgrounds)
Save changes and you might have to change to windows classic folders in folder options to get it to work.