Breaks my layout

That looks to me like a float issue, there needs to be a

stuck under there somewhere.

PS: This module is wonderful, it really helps make the input forms less confusing to people who don't know Drupal. Thanks ! :)

Crap. I mean to say there needs to be:

<div style="clear:both"></div>

stuck underneath the last floated item.

Figured it out - there's a very helpful function in vertical_tabs\vertical_tabs.js which calculates the height of the highest div and sets that as the wrapper height. However, the way jQuery accordion works, you don't need to do that - the div automatically resizes itself. So I just removed the whole thing, from line 23 down (from "//Find the height of the highest panel.")

So from the top:

// $Id: vertical_tabs.js,v 1.3 2008/03/07 17:31:18 ximo Exp $

/**
 * Vertical tabs node form layout (aka drawers).
 * @author Bevan Rudge drupal.geek.nz
 * @author Joakim Stai
 * @license GPL 2
 */

$(document).ready(function(){
  // Add wrapper for vertical tabs.
  $('#nodeform-buttons').before('<div id="nodeform-vertical-tabs"><ul class="ui-tabs-nav"></ul></div>');

  // Turn all marked fieldsets into vertical tabs.
  $('.nodeform-fieldset').each(function(i){
    $('#nodeform-vertical-tabs > ul').append('<li><a href="#' + $(this).attr('id') + '">' + $(this).find('legend').text() + '</a></li>');
    $(this).removeClass('collapsible collapsed').appendTo('#nodeform-vertical-tabs');
  });

  // Activate vertical tabs.
  $('#nodeform-vertical-tabs > ul').tabs();

});

Just replace vertical_tabs.js with this.

Just letting you know that this module has been discontinued, and that vertical_tabs by dmitrig01 is doing the vertical tabs much better than what I threw together in this one.