Could someone help me with this little bug?

I've got a website that works perfectly in mozilla and opera but when i try to view it with Internet Explorer my header is lower than where it was supposed to be and it looks really, really bad. i've attached two images with the differences between the browsers.

Here's the code where the header is inserted

<div class="site_header">
<div class="logo"><img src="<?php bloginfo('stylesheet_directory'); ?>/images/sitelogo.png" alt="sitelogo" width="616" height="85" /></div>
</div>
</div>

Code (markup):

and this is from the css

.site_header {
	float: left;
	height: 100px;
	width: 620px;
}

Code (markup):

any help would be appreciated

 

oh well, problem solved... apparently it's from IE6.