ขอความช่วยเหลือเกี่ยวกับ การตรวจสอบฟอร์ม (PHP + AJAX) ด่วนเลยครับ

<script type="text/javascript">
	var ajax = false;

	if(window.XMLHttpRequest) {
		ajax = new XMLHttpRequest();
		if(ajax.overrideMineType) {
			ajax.overrideMineType('text/html');
		}
	} else if(window.ActiveXObject) {
		try {
			ajax = new ActiveXObject('Msxml2.XMLHTTP');
		} catch(e) {
			try {
				ajax = new ActiveXObject('Microsoft.XMLHTTP');
			} catch(e) {
			}
		}
	}

	function ajaxLoad(method, url, data, displayID) {
		if(ajax == false) {
			alert('Cannot create XMLHTTP instance');
			return false;
		}
		ajax.open(method, url, true);
		ajax.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
		ajax.setRequestHeader('Content-length', data.length);
		ajax.setRequestHeader('Connection', 'close');
		ajax.onreadystatechange = function() {
			if(ajax.readyState == 3 && ajax.status == 200) {
				ajaxCallback(displayID, ajax.responseText);
			}
			if(ajax.readyState == 4 && ajax.status == 200) {
				ajaxCallback(displayID, ajax.responseText);
			}
		}
		ajax.send(data);
	}

	function ajaxCallback(displayID, responseText) {
		var el = document.getElementByID(displayID); //---> มีปัญหาที่นี่
		el.innerHTML = responseText;
	}

	function checkExpression(data, check, displayID) {
		var url = 'register-check-expression.php?ihash=' + Math.random();
		var data = 'email=' + encodeURI(data) + '&check=' + check;
		ajaxLoad('post', url, data, displayID);
	}
</script>

<?php
include("common.php");

$data = $_POST["data"];
$check = $_POST["check"];

if($check == "username") {
	$pattern = "^[a-z0-9_]{5, 15}$";
} else if($check == "email") {
	$pattern = "[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.([a-z]){2, 4})$";
	/*if(trim($data) == "") {
		//echo "<img src=\"images/false.png\" width=\"24\" height=\"24\" align=\"absmiddle\" />";
		exit();
	}
	$strSQL = "SELECT * FROM tbl_or_members WHERE email = '" . $data . "'";
	$objQuery = mysql_query($strSQL) or die ("Error Query [".$strSQL."]");
	$objResult = mysql_fetch_array($objQuery);
	if($objResult) {
		echo "<img src=\"images/false.png\" width=\"24\" height=\"24\" align=\"absmiddle\" />";
	} else {
		echo "<img src=\"images/true.png\" width=\"24\" height=\"24\" align=\"absmiddle\" />";
	}*/
}

if(!eregi($pattern, $data)) {
	//echo "<img src=\"images/false.png\" width=\"24\" height=\"24\" align=\"absmiddle\" />";
	echo "false";
} else {
	//echo "<img src=\"images/true.png\" width=\"24\" height=\"24\" align=\"absmiddle\" />";
	echo "true";
}
?>