Why doesn't this link show up?

Head out to http://www.hihatwebdesign.com/Trinity/header.php

I've got a link that's supposed to be showing up to the right of "Home." The url is images/about.png. It shows up fine as far as the integrity of the url, etc. But it doesn't show up correctly on the page.

Here's my html (I'm including only the part of the code that I'm thinking is crucial):

<div id="body_tray">
	<div id="header"><IMG SRC="images/header.png" usemap="#header" border="0"></div>
	<div id="nav_bar">
		<div id="nav_home"><IMG SRC="images/nav_home.png"></div>
		<div id="nav_about"><IMG SRC="images/nav_about.png"></div>
	</div>
	<div id="body_block">
		<div id="body_text"></div>
		<div id="left_column"><div id="cursor"></div><IMG SRC="images/carousel/side_student.png"></div>
		<div id="left_nav">
		<table cellspacing="0" cellpadding="0">
		<tr>
		<td>
		<A HREF="church_staff.php" class="staff"></a>
		</td>
		</tr>
		<tr>
		<td>
		<A HREF="directions.php" class="directions"></a>
		</td>
		</tr>
		<tr>
		<td>
		<A HREF="times.php" class="times"></a>
		</td>
		</tr>
		<tr>
		<td>
		<A HREF="directory.php" class="directory"></a>
		</td>
		</tr>
		<tr>
		<td>
		<A HREF="pastor.php" class="pastor"></a>
		</td>
		</tr>
		<tr>
		<td>
		<A HREF="media.php" class="gallery"></a>
		</td>
		</tr>
		<tr>
		<td>
		<A HREF="campus.php" class="campus"></a>
		</td>
		</tr>
		</table>
		</div>
	</div>
	<div id="footer"><IMG SRC="images/footer.png"></div>
</div>

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..and then here's my stylesheet:

#nav_bar {
position:relative;
margin:auto;
width:997px;
height:38px;
background-image:url(images/nav_bar.png);
background-repeat:no-repeat;
}

#nav_home {
position:relative;
margin-left:50px;
width:99px;
width:38px;
}

#nav_about {
position:relative;
margin-left:200px;
width:100px;
width:38px;
}

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Where am I blowing it? Why doesn't the "about" link show up at all?