Código HTML:
<form name="form4" method="post" target="mapawindow" action="mapa.php" onSubmit="MM_openBrWindow('','mapawindow','width=361,height=276')"> <select name="v" id="v" onChange="document.form4.submit()"> <option value="intsatus">Estados Unidos</option> <option value=".....">....</option> ...