procedure TForm1.Button1Click(Sender: TObject);
begin
   Application.HelpFile := 'MyHelpFile.hlp';
   Application.HelpCommand( HELP_FINDER, 0 );
end;

procedure HelpSearch;
var
  s: string;
begin
   s := '';
   Application.HelpFile := 'MyHelp.hlp';
   Application.HelpCommand( HELP_PARTIALKEY, LongInt( @s ) );
end;