Setting Help Window Size 

unit HelpUnit;
interface
uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls;
type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
var
  Form1: TForm1;
implementation
{$R *.DFM}
procedure TForm1.Button1Click(Sender: TObject);
var
 HelpWinInfo : THelpWinInfo;
begin
 With HelpWinInfo do
  begin
   wStructSize := SizeOf(HelpWinInfo);
   X  := 0;
   Y  := 0;
   DX := 256;
   DY := 256;
   wMax := SW_ShowNormal;
  end;
  Application.HelpFile := 'DEMO.HLP';
  Application.HelpCommand(HELP_SETWINPOS, LongInt(@HelpWinInfo));
  Application.HelpCommand(HELP_CONTENTS, 0);
end;
end.