Добавление своей кнопки к системным кнопкам окна.

procedure TForm1.DrawBtn;
var
WDc: HDc;
Cx,Cy: Integer;
XFrame, Yframe: Integer;
begin
WDc := GetWindowDc(Handle);
Cx := GetSystemMetrics(SM_CXSize);
Cy := GetSystemMetrics(SM_CYSize);
xFrame := GetSystemMetrics(SM_CXFrame);
yFrame := GetSystemMetrics(SM_CYFrame);
R := Bounds(Width - xFrame - 4*Cx + 2, yFrame + 2, Cx - 2, Cy - 4);
if Press then
DrawFrameControl(WDc,R,DFC_BUTTON,DFCS_ButtonPUSH or DFCS_PUSHED)
else
DrawFrameControl(WDc,R,DFC_BUTTON,DFCS_ButtonPUSH);
ReleaseDc(Handle,WDC);
end;