You could use something like this to parse the URI:
http://blog.stevenlevithan.com/archives/parseuri
Then you can access the parameters easily from the parent page:
// Set the link that we want to load/examine
var link = 'page?foo=bar';
// Load the link content (as per your code)
div.load(link);
// Grab whatever variables we want from the link
var uri = parseUri(link);
var foo = uri.queryKey.hasOwnProperty('foo') ? uri.queryKey.foo : false;
alert(foo);
EDIT:
As bfavaretto already commented, the content loaded in via AJAX is just a string. It's not a page that will be aware of its URI.
However, if you really want the loaded content to be able to access its URI, just make it available in the content itself. For example:
$('#my_div').load('page?foo=bar)
And in the content of "page?foo=bar":
<div class="container" data-page-uri="{{ insert uri here with php, ruby, whatever }}">
<!-- my page content -->
</div>
Now in your loaded content, you can determine the URI by finding the relevant div with the "data-page-uri" data attribute. Once you have the link, you said that you know how to grab the parameters from it...
Hope that helps.