Something

var net=new Object();
net.READY_STATE_UNINITIALIZED=0;
net.READY_STATE_LOADING=1;
net.READY_STATE_LOADED=2;
net.READY_STATE_INTERACTIVE=3;
net.READY_STATE_COMPLETE=4;

net.ContentLoader=function(url,onload,onerror,method,params,contentType) {
	this.url=url;
	this.req=null;
	this.onload=onload;
	this.onerror=(onerror) ? onerror: this.defaultError;
	this.loadXMLDoc(url,method,params,contentType);
}

net.ContentLoader.prototype= {
	loadXMLDoc:function(url,method,params,contentType) {
		if(!method) {
			method="GET";
		}
		if(!contentType && method=="POST")
		{
			contentType="application/x-www-form-urlencoded";
		}
		if(window.XMLHttpRequest) {
			this.req=new XMLHttpRequest();
		} else if (window.ActiveXObject) {
			this.req=new ActiveXObject("Microsoft.XmlHttp");
		}
		if(this.req) {
			try {
				var loader=this;
				this.req.onreadystatechange=function() {
					loader.onReadyState.call(loader);
				}
				this.req.open(method,url,true);
				if(contentType) {
					this.req.setRequestHeader("Content-Type", contentType);
				}
				this.req.send(params);
			} catch (err) {
				this.onerror.call(this);
			}
		}
	},
	onReadyState:function() {
		var req=this.req;
		var ready=req.readyState;
		if (ready==net.READY_STATE_COMPLETE) {
			var httpStatus=req.status;
			if (httpStatus==200 || httpStatus==0) {
				if(this.onload != null) {
					this.onload.call(this);
				}
			} else {
				this.onerror.call(this);
			}
		}
	},
	defaultError:function() {
		alert("error fetching data!" + "\n\nreadyState: "+this.req.readyState+"\nstatus: "+this.req.status+"\nheaders: "+this.req.getAllResponseHeaders());
	}
}