Hola 6793 :)
Esta es una forma de lograrlo:
<html>
<head>
<title>Something</title>
<SCRIPT>
// Variables...
URLArray = new Array();
URLArray[0] = "";
URLArray[1] = "http://www.microsoft.com";
URLArray[2] = "http://www.netscape.com";
URLArray[3] = "http://www.maestrosdelweb.com";
</SCRIPT>
<SCRIPT FOR=selector EVENT=onchange>
if (this.selectedIndex == 0) return true;
location.assign(URLArray[this.selectedIndex]);
this.selectedIndex = 0;
</SCRIPT>
</HEAD>
<BODY>
<SELECT ID="selector">
<OPTION Value=0 SELECTED>Elija un sitio para ir
<OPTION Value=1>Microsoft
<OPTION Value=2>NetScape
<OPTION Value=3>Maestros del Web
</SELECT>
</BODY>
</html>
Suerte ;)
<IMG src=banderas/argentina.gif>