I've got a web application, consisting mainly of a big form with information. The form is split into multiple tabs, to make it more readable for the user:

<form>
<div id="tabs">
  <ul>
    <li><a href="#tab1">Tab1</a></li>
    <li><a href="#tab2">Tab2</a></li>
  </ul>
  <div id="tab1">A big table with a lot of input rows</div>
  <div id="tab2">A big table with a lot of input rows</div>
</div>
</form>

The form is dynamically extended (extra rows are added to the tables). Every 10 seconds the form is serialized and synchronized with the server.

I now want to add an interactive form on one of the tabs: when a user enters a name in a field, this information is sent to the server and an id associated with that name is returned. This id is used as an identifier for some dynamically added form fields.

A quick sketchup of such a page would look like this:

<form action="bigform.php">
<div id="tabs">
  <ul>
    <li><a href="#tab1">Tab1</a></li>
    <li><a href="#tab2">Tab2</a></li>
  </ul>
  <div id="tab1">A big table with a lot of input rows</div>
  <div id="tab2">
    <div class="associatedinfo">
    <p>Information for Joe</p>
    <ul>
      <li><input name="associated[26][]" /></li>
      <li><input name="associated[26][]" /></li>
    </ul>
    </div>

    <div class="associatedinfo">
    <p>Information for Jill</p>
    <ul>
      <li><input name="associated[12][]" /></li>
      <li><input name="associated[12][]" /></li>
    </ul>
    </div>
    <div id="newperson">
      <form action="newform.php">
        <p>Add another person:</p> 
        <input name="extra" /><input type="submit" value="Add" />
      </form>
    </div>
  </div>
</div>
</form>

The above will not work: nested forms are not allowed in HTML. However, I really need to display the form on that tab: it's part of the functionality of that page. I also want the behaviour of a separate form: when the user hits return in the form field, the "Add" submit button is pressed and a submit action is triggered on the partial form.

What is the best way to solve this problem?