4 colum design using container help please

Hello, im a currentlly developing a drupal theme and need some help. I am using a container to put the left side bar, content, and the right side bar in. When i try to add in another sidebar to act as ads on the right, it wont show up...

Bellow i have included some code were i insert the colums.

CSS code:

#container {
}
#container #left {
	width:120px;
	float:left;
	background:#e4e4e4;
	padding:10px;	
}
#container #ad {
	width:290px;
	padding:10px;	
	margin 0px 160px 0px 540px;
	background:#e4e4e4;
}
#container #right {
	width:150px;
	float:right;
	background:#e4e4e4;
	padding:10px;
}
#container #content {
	margin:0px 410px 0px 120px;
}

Now the width is 1000 for now.

The page.tpl.php code:

<div id="container">

<?php if ($sidebar_left != ""): ?>
<div id="left"><?php print $sidebar_left ?></div>
<?php endif; ?>

<?php if ($sidebar_ad != ""): ?>
<div id="ad"><?php print $sidebar_ad ?></div>
<?php endif; ?>

<?php if ($sidebar_right != ""): ?>
<div id="right"><?php print $sidebar_right ?></div>
<?php endif; ?>

<div id="content">
<?php if ($title) { ?><h1><?php print $title ?></h1><?php } ?>
<div id="tabs"><?php print $tabs ?></div>
<?php print $help ?>
<?php print $messages ?>
<?php print $content; ?>
</div></div>

Now as you see i have 4 colums set. Now at the moment only sidebar_left, content, and sidebar_right show

Sidebar_ad will not show

Any ideas guys??

Thanks