easy. just simply use the XMLHTTP object
code:
var xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
xmlhttp.open("GET","http://url.com/xml.xml",false);
xmlhttp.send(null);
var xml = xmlhttp.responseXML;
var Peter = xml.selectNodes("/Family/Member/Age/text()");
/*
either
var Peter = xml.selectNodes("/Family/Member/Age/text()");
or
var Peter = xml.selectNodes("/Family/Member/Age/text()")[0];
.. haven't used this function much
*/