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procedure WMNCPAINT(var Msg: TMessage); Message WM_NCPAINT;

[...]

procedure TForm1.WMNCPAINT(var msg: TMessage);
var
  rect: TRect;
  dc: HDC;
  szBuffer: array[0..255] of Char;
begin
  Inherited;
  if Msg.Msg = WM_NCPAINT then
  begin
    dc := GetWindowDC(Handle);
    rect.Left := GetSystemmetrics(SM_CXEDGE);
    rect.Top := GetSystemmetrics(SM_CYEDGE);
    rect.Right := Form1.Width-GetSystemmetrics(SM_CYEDGE);
    rect.Bottom := Getsystemmetrics(SM_CYCAPTION)+GetSystemmetrics(SM_CYFRAME);
    lstrcpy(szBuffer, 'Meine Fenstercaption');
    SetBkMode(dc, TRANSPARENT);
    SetTextColor(dc, RGB(255,255,255));
    DrawText(dc, szBuffer, lstrlen(szBuffer), rect, DT_CENTER or DT_VCENTER);
    ReleaseDC(Handle, dc);
  end;
  ReleaseDc(Handle, dc);
end;