horizontal centering of image in <td> with css generated drop shadow

looking to center an image that is using a css generated drop shadow with negative margins and float:left;

i'm using tables as opposed to pure css because of the cms we're plugging this into.

here's the link:

http://ctemps.cjehost.com/thumbs2_table.php

notice how the thumbnails are horizontally aligned to the left-i need them to horizontally align center.  i'm sure it's the float:left and negative margins that are throwing me for a loop here. but, short of rethinking my drop shadow styles can anyone think of a quick fix here??

/*GALLERY DROP SHADOW*/
.img-shadow {
float:left;
background: url(../images/drop_shadow.png) no-repeat bottom right !important;
background: url(../images/drop_shadow.png) no-repeat bottom right;
margin: 10px 0 0 10px !important;
margin: 10px 0 0 5px;
}
/*GALLERY IMAGE href*/
a.imgOver img:hover{
background-color: #b81652;
}
a.imgOver img{
display: block;
position: relative;
margin: -10px 1px 1px -10px;
padding: 4px;
}
 
html:
 
<td height="136" width="136" align="center">
						<div class="img-shadow"><a href="#" class="imgOver"><img src="images/fpo_thumb_num4.jpg" border="0" /></a></div></td>

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