Help with Javascript Error: getElementsByTagName is null or not an object

<!--
function TJK_quote(){// v1.1.2 Copyright (c) 2006 TJKDesign - Thierry Koblentz
// use the same paths for: SRC and STYLE (filter) attributes
// set top padding values to match the height of your images
// you may style both images using CSS: blockquote img {...}
// or individually using classes:  .q_O {...} and .q_C {...}
if (!document.getElementsByTagName || !document.createElement) return;
	var z_Q=document.getElementsByTagName("blockquote");
	for (var x=0;x<z_Q.length;x++){
	var q_O = document.createElement('img');
	q_O.alt="";
	q_O.src="/img/q_O.png";
	q_O.style.filter="progid:DXImageTransform.Microsoft.AlphaImageLoader(enabled='true',src='/img/q_O.png')";
	if (document.all) q_O.style.paddingTop="15px";	
	q_O.style.verticalAlign="text-bottom";	
	q_O.className="q_O";	
	var q_C = document.createElement('img');
	q_C.alt="";
	q_C.src="/img/q_C.png";	
	q_C.style.filter="progid:DXImageTransform.Microsoft.AlphaImageLoader(enabled='true',src='/img/q_C.png')";
	if (document.all) q_C.style.paddingTop="15px";	
	q_C.style.verticalAlign="top";	
	q_C.className="q_C";		
	z_Q[x].getElementsByTagName("p")[0].insertBefore(q_O,z_Q[x].getElementsByTagName("p")[0].firstChild)
	z_Q[x].getElementsByTagName("p")[0].appendChild(q_C);
	var z_URL=z_Q[x].getAttribute("cite");
	if (z_URL){
		var z_DIV = document.createElement('div');
		var z_FROM = document.createTextNode("Quote from: ");
		z_Q[x].appendChild(z_DIV);
		z_DIV.className="q_D";
		var z_A = document.createElement('a');
		var z_DOMAIN = document.createTextNode(z_URL.slice(z_URL.indexOf("//")+2,z_URL.indexOf("/",9)));
		z_A.href=z_URL;
		z_A.appendChild(z_DOMAIN);
		z_DIV.appendChild(z_FROM);
		z_DIV.appendChild(z_A);
		}

	}
}
//-->