To create a window with rounded corners or a tab control without a surrounding window, it would be great if i could set the transparency of the FP Window to 100% and all other elements to 0%!
You can call functions from the Windows API to make one color in the window completely transparent (it will actually allow you to click behind the window). See here for a simplistic example. The "crkey" input in the last DLL call is the transparent color.