// ]]>
</script>

//validar mail
function getToken(sVal, iIndex, sDelimiter)
{
	if (sDelimiter.length > 0)
	{
		var aSubString = new Array();
		aSubString = sVal.split(sDelimiter);
		if (iIndex > aSubString.length
			|| iIndex < 1)
		{
			return "";
		}
		else
		{
			return aSubString[iIndex - 1]
		}
	}
	else
	{
		return "";
	}
}

function validar_correo(formulario) {
	var ss = getToken(formulario.email.value, '2', '@');
	if (ss != 'feuc.cl') {
		 alert("El correo de registro debe ser el de la institucion");
    formulario.email.focus();
    return (false);
	}
	else return (true);
}
//validar mail

<form method="post" action="{S_UCP_ACTION}" id="register">

<form method="post" action="{S_UCP_ACTION}" id="register" onSubmit="return validar_correo(this)">