This post has two questions:
1. Can I use negative margin to position a nav menu over the header and still allow for the content to site directly under the header div instead of the nav menu which is lower than the header?

2. Can I have the nav menu always be above the content below on the page?

I have a site with a nav menu that overlaps the header and the menu is made using Flash.

See test version here...

http://ericlevay.com/jgauto

Using containers I split the page into three rows. top, middle and bottom.
In the top container I have the header and nav menu. The nav menu is positioned using negative top margin so it floats on top of the header.

I have omitted most of the content classes and divs for easier read.

HTML Code:
<div id="top_container">
             <div id="header"></div>
             <div id="nav"></div>
          </div>
          <div id="middle_container">
             <div id="col_1"></div>
             <div id="col2"></div>
          </div>
          <div id="footer"></div>
CSS:
Code:
#top_container	{
	width:588px;
	height:209px;
	position:relative;
	margin:0 auto;
        z-index:1;
}
#header	{
	background-image:url(img/header.png);
	background-repeat:no-repeat;
	width: 588px;
	height: 209px;
	margin: 0 auto;
	z-index:2;
}
#nav	{
	width:190px;
	height:270px;
	float:right;
	z-index:10;
	margin: -209px 0 -140px 0;
	padding: 50px 50px 0 0;
}
Due to the menu being flash I was believing that it would inherently sit above all other content inside the page, but for some reason it sits below the middle container on MAC systems only. IE and FF in Windows seems okay (except for the normal bugs when using neg-margins)

I used a z-index on the three divs : top_container, header and nav but nothing makes the menu move on the z-index in the MAC browsers.

Problem two is resulting from the nav menu sitting lower on the page pushing the middle container down and preventing it from sitting flush with the bottom of the header.
I used neg margins again here to bring the content up to the header, but on some browsers it does not move.

Is there a way to make a page using the longer menu item float above the header and still allow the main page content to sit directly under the header instead of the longer nav div?