function revista()
{
	var num = document.anteriores.elegirNum.value;
	eval ("window.open('http://www.mapfre.com/mapfreasistencia/es/siam/n"+num+"/home.html')")
} 

document.write("<table border='0' cellpadding='0' cellspacing='0'><form name='anteriores'><tr>");
document.write("<td align='right' valign='bottom' width='100%'><select name='elegirNum' onchange='revista()' class='comboBox'>");
	document.write("<option value=''>Numeros anteriores</option><option value='20'>nš 20</option></option>");
document.write("</select></td></tr></form></table>");