{$R *.DFM}

procedure SetRes(XRes, YRes: DWord);
var
lpDevMode : TDeviceMode;
begin
EnumDisplaySettings(nil, 0, lpDevMode);
lpDevMode.dmFields:=DM_PELSWIDTH or DM_PELSHEIGHT;
lpDevMode.dmPelsWidth:=XRes;
lpDevMode.dmPelsHeight:=YRes;
ChangeDisplaySettings(lpDevMode, 0);
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
SetRes(800,600);
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
SetRes(1024,768);
end;