As I expected, the background which is custom rendered draws fine, but the buttons render like XP renders them on default, because there is no custom drawing done there. (I didn't do that because the standard Vista ToolStripButton background is the same as the buttons used in these 'special' toolstrips (possibly even exactly the same).

If I find the time to continue with this control (custom drawing takes a lot of patience, finding the right colors and 'sizes' and stuff.. ) I'll try to do the button backgrounds custom drawn too, that will make it work on XP better.