First, thanks to all who posted after I said thanks the last time.

"Am I right, that you created the buttons/controls with the winapi, made them somehow "invisible" and created a graphics representation of each state in the engine?"
You are wrong.
I programmed the buttons and all other controls completely myself. They act like Windows buttons, because I examined the behaviour of the Windows buttons and made my buttons do the same.


Maybe I'll make a GUI editor some time, but not in the near future...