Jquery continuing....

Well, still having fun with Jquery.  I'm curious though if there are any experts out there that have used Jquery in an application that involves downloading and uploading files?  We've been experimenting with it and found that uploading and downloading involves more than I thought.   The biggest hurdle with this is associative arrays.  As soon as I can figure out the best way to handle this, will post.  If you know easy ways to do this please do post!  Thanks.