function login_check()
{
	if(document.frm_login.email.value=='')
	{
		alert("¡Por favor, introduzca su email!");
		document.frm_login.email.focus();
		return false;
	}

	else if(document.frm_login.email.value!='')
	{
		if(!validateEmail(document.frm_login.email.value))
		{
			alert("Por favor, introduzca un email válildo.");
			document.frm_login.email.focus();
			return false;
		}	
		
	}
	if(document.frm_login.password.value=="")
	{
		alert("Por favor, introduzca su contraseña");
		document.frm_login.password.focus();
		return false;
	}
	return true;
}

function validateEmail(email)
{
// a very simple email validation checking. 
// you can add more complex email checking if it helps     
    var splitted = email.match("^(.+)@(.+)$");
    if(splitted == null) return false;
    if(splitted[1] != null )
    {
      var regexp_user=/^\"?[\w-_\.]*\"?$/;
      if(splitted[1].match(regexp_user) == null) return false;
    }
    if(splitted[2] != null)
    {
      var regexp_domain=/^[\w-\.]*\.[A-Za-z]{2,4}$/;
      if(splitted[2].match(regexp_domain) == null) 
      {
	    var regexp_ip =/^\[\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\]$/;
	    if(splitted[2].match(regexp_ip) == null) return false;
      }// if
      return true;
    }
return false;
}