AJAX check for changes

I currently have a page with a setInterval() timer set to refresh a div every 60s. I'm wondering how i can check to see if there are any changes, and only if there are, then use ajax to reload the div. Also, is there any way to compare the current contents of the div to what the new contents would be and only update the changes? Here is my current js code:

function ajaxReload(){
	var ajaxRequest;  // The variable that makes Ajax possible!
	
	try{
		// Opera 8.0+, Firefox, Safari
		ajaxRequest = new XMLHttpRequest();
	} catch (e){
		// Internet Explorer Browsers
		try{
			ajaxRequest = new ActiveXObject("Msxml2.XMLHTTP");
		} catch (e) {
			try{
				ajaxRequest = new ActiveXObject("Microsoft.XMLHTTP");
			} catch (e){
				// Something went wrong
				alert("Your browser broke!");
				return false;
			}
		}
	}
	// Create a function that will receive data sent from the server
	ajaxRequest.onreadystatechange = function(){
		if(ajaxRequest.readyState == 4){
			var ajaxDisplay = document.getElementById('ajaxDiv');
			ajaxDisplay.innerHTML = ajaxRequest.responseText;
		}
	}
	
	ajaxRequest.open("GET", "outlive2.php" , true);
	ajaxRequest.send(null); 
}
setInterval("ajaxReload()", 60000);

Code (markup):

Thanks
-Matt