http_request failing between sites

im trying to call a page on "Server B" from "Server A" using http_request method. the problem is the request fails at http_request.open(). Below is the very basic code im using that can be found everywhere online.

Code Calling from a page on Server (site) A. Requesting URL is on Server (site) B

makeRequest('http://www.sitename.com/ajax_insert.php?field_name=test&field_value=',this.value);

This is the code in the makeRequest() function which is on Server (site) A.

function makeRequest(url, parameters) {

http_request = false;
if (window.ActiveXObject) { // IE
	try {
		http_request = new ActiveXObject("Msxml2.XMLHTTP");
	} catch (e) {
		try {
			http_request = new ActiveXObject("Microsoft.XMLHTTP");
		} catch (e) {}
	}
} else if (window.XMLHttpRequest) {// Mozilla, Safari,...xmlHttpReq.overrideMimeType
	http_request = new XMLHttpRequest();
	if (http_request.overrideMimeType) {
		// set type accordingly to anticipated content type
		http_request.overrideMimeType('text/xml');
	}else{ alert('Did not create *http_request.overrideMimeType*'); return false; }
} 

if (!http_request) {

	alert('Cannot create XMLHTTP instance');
	return false;

}

http_request.onreadystatechange = alertContents;

// FOR GET VARS
http_request.open('GET', url + parameters, true);
http_request.send(null);

}

So what am i missing? How can i get the http_request to process a page on another server (site). FYI, outside this application, my code as written works fine.

Thank you much for all the help.

Think of the security implications that allowing cross domain AJAX would bring.

AJAX is [currently] limited to the domain from which it's being served.

what you need to do is create a php page that reads data from a remote server and put it in a string

then after that you can call the local php script to read data from a remote server. It works like a charm

as corbin said you can only read data from the same domain with javascript but php can read remote data

what you need to do is create a php page that reads data from a remote server and put it in a string

Can you expand your suggestion a little. I think i get it, but would like a little more info

Your ajax calls a local PHP page on your server.  On that page you would do the same that you're trying to attempt with Ajax, but have php do it and put the content you're pulling on the screen.  Your Ajax takes it from your php page so that you don't violate Ajax security settings.

[Local Ajax]->[Local PHP Page/script]->(Remote Page)->[back to Local PHP Page/Script]-[Local Ajax]

instead of your:

[Local Ajax]--x-->(Remote Page)--x-->[Local Ajax]

which isn't allowed.

The php script does the fopen, or whatever you need to get data off that remote page.