I've used a jQuery plugin called jQuery.query that can manipulate URLs. If memory serves correct you do something along the lines of $.query.set('var', value) to set querystring values. And $.query.get('var') to retrieve.
Sadly the jQuery team seems to have taken down the jQuery plugins site and I can't seem to find any other links to the source. Even the author's site<http://blairmitchelmore.com/jquery>just links back to the jQuery plugins site :\ I might be able to dig up a copy to send you if you're interested. ~Brian