program iexplor;

uses
  Windows, OLEAuto;

procedure OpenInternetExplorer( sURL : string );
const
  csOLEObjName = 'InternetExplorer.Application';
var
  IE: Variant;
  WinHanlde: HWnd;
begin
  if VarIsEmpty(IE) then
  begin
    IE := CreateOleObject(csOLEObjName);
    IE.Visible := true;
    IE.Navigate(sURL);
  end
  else
  begin
    WinHanlde := FindWIndow('IEFrame', nil);
    if 0 <> WinHanlde then
    begin
      IE.Navigate(sURL);
      SetForegroundWindow(WinHanlde);
    end
    else
    begin
      // handle error ...
    end;
  end;
end;

begin
  OpenInternetExplorer('microsoft.com');

end.