I would assume I would also have to alter the PHP file slightly? How would I do that? Would it be tpl_header.php?
Yes, this is the file where the image map would be if you choose to do it this way.
Here is a generic sample and spacer.gif is a 1pixel transparent image that you would have to create and I recall that I added the div "navHead". You need to provide the href's and the alt text and adjust to match your background image.
Code:
<!--bof-branding display-->
<div id="logoWrapper">
<div id="logo"><?php echo '<a href="' . HTTP_SERVER . DIR_WS_CATALOG . '">' . zen_image($template->get_template_dir(HEADER_LOGO_IMAGE, DIR_WS_TEMPLATE, $current_page_base,'images'). '/' . HEADER_LOGO_IMAGE, HEADER_ALT_TEXT) . '</a>'; ?></div>
<!-- begin top navigation -->
<div id="navHead">
<img src="includes/templates/test/images/spacer.gif" width="235" height="44" border="0" /></a><a href="index.php?main_page=?Ref1?">
<img src="includes/templates/test/images/spacer.gif" alt="?Some_Text?" width="120" height="44" border="0" /></a><a href="index.php?main_page=?Ref2">
<img src="includes/templates/test/images/spacer.gif" alt="?Some_Text?" width="125" height="44" border="0" /></a><a href="index.php?main_page=index&cPath=5">
<img src="includes/templates/test/images/spacer.gif" alt="Accessories" width="125" height="44" border="0" /></a><a href="index.php?main_page=about_us">
<img src="includes/templates/test/images/spacer.gif" alt="About Us" width="120" height="44" border="0" /></a>
<!-- end top nav --></div>
</div>