I have three forms on a page. They each have multiple inputs including files. I would like so that when I submit the last form, the inputs for all three forms are sent to
Your only option right now is a jQuery AJAX request (or a XMLHTTP one, but that's not recommended).
Try rethinking your design, I mean, why do you need 3 forms on one page... that's too `formy' for me already.
There is something else you can probably do: put the jQuery UI dialog box container div inside one form (this should work, I guess) and just have the fields within it...