[NumLock]

проще некуда:

Код:

var
  doc: IHTMLDocument3;
begin
  doc:=WebBrowser1.Document as IHTMLDocument3;
  (doc.getElementById('select_id') as IHTMLSelectElement).selectedIndex:=UpDown1.Position;
  (doc.getElementById('select_id') as IHTMLElement).click;
end;

http://zalil.ru/34428576