Figured it out. Here's the info in case you're curious:
Code:
{if $product.manufacturerid ne ""}
<table cellspacing="0" cellpadding="0" border="0" width="800">
<tr>
<td>[img]{$ImagesDir}/spacer.gif[/img]</td>
</tr>
<tr>
<td>[img]{$ImagesDir}/header/header_{$product.manufacturerid}.jpg[/img]</td>
</tr>
</table>{/if}
Modify the HTML to your needs.
