this is taken directly from my game so im not sure if its any use for you.


to change the screen res....

Code:
var
  dmScreenSettings : DEVMODE;

...

  if Fullscreen then
  begin
    ZeroMemory(@dmScreenSettings, SizeOf(dmScreenSettings));
    with dmScreenSettings do begin
      dmSize       := SizeOf(dmScreenSettings);
      dmPelsWidth  := Width;
      dmPelsHeight := Height;
      dmBitsPerPel := PixelDepth;
      dmFields     := DM_PELSWIDTH or DM_PELSHEIGHT or DM_BITSPERPEL;
    end;


    if (ChangeDisplaySettings(dmScreenSettings, CDS_FULLSCREEN) = DISP_CHANGE_FAILED) then
    begin
      MessageBox(0, 'Unable to switch to fullscreen!', 'Error', MB_OK or MB_ICONERROR);
      Fullscreen := False;
    end;
  end;
and to set it back...

Code:
  if Fullscreen then
  begin
    ChangeDisplaySettings(devmode(nil^), 0);
    ShowCursor(True);
  end;

hope it helps