function check_form(f)
    {
    	for(var i = 0; i < document[f].elements.length; i++)
    	{
    		if ((document[f].elements[i].type != "hidden" && document[f].elements[i].type != "checkbox") && (document[f].elements[i].value == ""))
    		{
    			alert("Por favor ingrese "+ document[f].elements[i].title);
    			document[f].elements[i].focus();
    			return false;
    		}
    	}
		m=check_email(document[f].email.value);
		if(m==false)
		{
			document[f].email.focus();
			return false;
		}
		return true;
    }
    
    function check_email(mailObj)
    {
     var decadr, decdomaine, nbparties, longdernpartie;
    
     if(mailObj.search(/ /) != -1)
      {alert("E-mail: no se permiten espacios");
       return false;
      }
     decadr = mailObj.split('@');
     if(decadr.length != 2 || decadr[0] == "" || decadr[1] == "")
      {alert("E-mail: formato debe ser usuario@dominio.xxx");
       return false;
      }
     decdomaine = decadr[1].split('.');
     nbparties=decdomaine.length;
     if(nbparties > 1)
     { longdernpartie=decdomaine[nbparties-1].length;
       if((longdernpartie != 2) && (longdernpartie != 3))
    	{ 
			alert("E-mail: Dominio incorrecto, solo 2 o 3 letras despues del punto");
    	  	return false;
    	}
     }
     else
     { 
	 	alert("E-mail: Falta dominio");
      	return false;
     }
     return true;
    }