Hi question about storing contents of a file

Hi, i'm quite new in javascript....
I found a script which reads tha contents of a file stored on the web server and prints it on screen like an include.. i want to modify this script so the contents of the file stored on a javascript variable. the script is the following:

<SCRIPT LANGUAGE="JavaScript">

// new prototype defintion
document.include = function (url) {
if ('undefined' == typeof(url)) return false;
var p,rnd;
if (document.all){
// For IE, create an ActiveX Object instance
p = new ActiveXObject("Microsoft.XMLHTTP");
}
else {
// For mozilla, create an instance of XMLHttpRequest.
p = new XMLHttpRequest();
}
// Prevent browsers from caching the included page
// by appending a random number
rnd = Math.random().toString().substring(2);
url = url.indexOf('?')>-1 ? url+'&rnd='+rnd : url+'?rnd='+rnd;
// Open the url and write out the response
p.open("GET",url,false);
p.send(null);
document.write( p.responseText );
}
</SCRIPT>

and for printing the contets of the file i must write inside the body of my
<script>
document.include('header.inc');
</script>

i just want to strore the contents on a variable and not print them

thanks a lot for your time