$xoops_module_header should go between the head and /head tags. see this code snippet here
<head>
<meta http-equiv="content-type" content="text/html; charset=<{$xoops_charset}>" />
<meta http-equiv="content-language" content="<{$xoops_langcode}>" />
<meta name="robots" content="<{$xoops_meta_robots}>" />
<meta name="keywords" content="<{$xoops_meta_keywords}>" />
<meta name="description" content="<{$xoops_meta_description}>" />
<meta name="rating" content="<{$xoops_meta_rating}>" />
<meta name="author" content="<{$xoops_meta_author}>" />
<meta name="copyright" content="<{$xoops_meta_copyright}>" />
<meta name="generator" content="XOOPS" />
<title><{$xoops_sitename}> - <{$xoops_pagetitle}>title>
<link href="<{$xoops_url}>/favicon.ico" rel="SHORTCUT ICON" />
<link rel="stylesheet" type="text/css" media="screen" href="<{$xoops_url}>/xoops.css" />
<link rel="stylesheet" type="text/css" media="screen" href="<{$xoops_themecss}>" />
<{$xoops_module_header}>
<script type="text/javascript">
script>
head>
<body>
Count 8 lines up from body- you will see $xoops_module_header.
No title
To Add To This FAQ..
FAQ: I've modified my theme, but why cant I see the changes?
if you follow all the steps.. you will definitely see the modified theme. (a bit extreme. though)
just doing step one.. & revisit the page/theme/template on your site.. maybe a click on the refresh button and the changes would show (most of the times).. and don't forget to turn the setting back to no.