[ChristGuy]

Greetingz...

Firstly try (It's not PHP but it works...):

PHP Code:

<SCRIPT LANGUAGE="JavaScript">

  function checkData()

  {

    if (document.myForm.TelNo1.value == document.myForm.TelNo2.value)

    {

      return true;

    }

    else

    {

      alert("Please enter the same telephone number");

      return false;

    }

  }

</SCRIPT>

<FORM ACTION="proccessform.php" NAME="myForm" onSubmit="return checkData()">

  Name: <INPUT TYPE="TEXT" NAME="Name"><BR>

  Tel1: <INPUT TYPE="TEXT" NAME="TelNo1"><BR>

  Tel2: <INPUT TYPE="TEXT" NAME="TelNo2"><BR>

  <INPUT TYPE="SUBMIT" NAME="btnSubmit"><BR>

</FORM> 

Secondly the following is used in the Handler script of the form:

PHP Code:

<?php

  if ($_POST['TelNo1'] != $_POST['TelNo2'])

  {

    echo "error";

  }

?>

Hope that helps...