function ValidaLogin(theForm)
{

if (Trim(theForm.usuario_login.value) == "")
 {
  alert("Por favor, Digite o nome do Usuário")
  theForm.usuario_login.focus();
    return (false);
  }
if (Trim(theForm.senha_login.value) == "")
 {
  alert("Por favor, Digite sua Senha")
  theForm.senha_login.focus();
    return (false);
  }  
  
  return (true);
}

function Trim(s) 
{
  // Remove leading spaces and carriage returns
  while ((s.substring(0,1) == ' ') || (s.substring(0,1) == '\n') || (s.substring(0,1) == '\r'))
  {
    s = s.substring(1,s.length);
  }

  // Remove trailing spaces and carriage returns
  while ((s.substring(s.length-1,s.length) == ' ') || (s.substring(s.length-1,s.length) == '\n') || (s.substring(s.length-1,s.length) == '\r'))
  {
    s = s.substring(0,s.length-1);
  }
  return s;
}