This program demonstrates using a bitmap as your dialog.
Whatever part of your dialog you color with the color you define will be transparent (creating the rounded corners and holes in the window). And also it simplifies the changing of colors/bitmaps on buttons when you put the mouse over it and when it has focus, etc with the BtnSt class. Just run the program if that doesn't make any sense.
No credit belongs to me. The BtnSt class and the function that actually does all the bitmap/region work (DIBToRgn()) is stuff I found on CodeGuru.
I figure it could help somebody. It helped me.