Did you manage to get any further with this?
I also need to do the same thing, I would like to let a visitor sort the posts by title, date or a custom field by selecting the sort type from a dropdown list on the webpage. I can’t seem to find anything that helps much. I know you can use the orderby in the query_posts in the template. but how do you get the users selection in the query_posts and then the resulting update of the webpage after selection, is where I am stuck.
Can anybody help with this?