Amazing.
I have produced a page that is Valid XHTML 1.0 Transitional using DNN3.
Have a look on the W3C Validatior, it's amazing, it validates...
http://validator.w3.org/
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
<head id="Head">
<title>
My Website > Home ( DNN 3.2.2 )
</title>
<meta name="DESCRIPTION" content="My Website"/>
<meta name="KEYWORDS" content="DotNetNuke, DNN, Content, Management, CMS,DotNetNuke,DNN"/>
<meta http-equiv="PAGE-ENTER" content="RevealTrans(Duration=0,Transition=1)"/>
<link id="_DotNetNuke_Portals__default_" rel="stylesheet" type="text/css" href="/DotNetNuke/Portals/_default/default.css"></link><link id="_DotNetNuke_Portals__default_Skins_xhtml_" rel="stylesheet" type="text/css" href="/DotNetNuke/Portals/_default/Skins/xhtml/skin.css"></link><link id="_DotNetNuke_Portals_0_" rel="stylesheet" type="text/css" href="/DotNetNuke/Portals/0/portal.css"></link>
<script type="text/javascript" src="/dotnetnuke/js/dnncore.js"></script>
</head>
<body id="Body">
<noscript>
</noscript>
<form name="form" method="post" action="/DotNetNuke/default.aspx" id="form" enctype="multipart/form-data" style="height: 100%;">
<div id="sidebar">
<div id="menu">
<span id="dnn_dnnLINKS_lblLinks"><a class="SkinObject" href="http://localhost/DotNetNuke/Home/tabid/36/Default.aspx">Home</a> <a class="SkinObject" href="http://localhost/DotNetNuke/W3C/tabid/59/Default.aspx">W3C</a></span>
</div>
<a id="dnn_dnnLOGIN_hypLogin" class="SkinObject" href="http://localhost/DotNetNuke/Home/tabid/36/ctl/Login/Default.aspx">Login</a>
<br />
<a id="dnn_dnnUSER_hypRegister" class="SkinObject" href="http://localhost/DotNetNuke/Home/tabid/36/ctl/Register/Default.aspx">Register</a>
</div>
<div id="dnn_ControlPanel"></div>
<div id="content">
<div id="dnn_ContentPane"><a name="373"></a>
<div>
<div id="dnn_ctr373_ContentPane" align="left"><!-- Start_Module_373 --><div id="dnn_ctr373_ModuleContent">
<span id="dnn_ctr373_HtmlModule_HtmlHolder" class="Normal">
Some Content
</span><!-- End_Module_373 -->
</div></div>
</div>
<a name="375"></a>
<div>
<div id="dnn_ctr375_ContentPane" align="left"><!-- Start_Module_375 --><div id="dnn_ctr375_ModuleContent">
<span id="dnn_ctr375_HtmlModule_HtmlHolder" class="Normal">
<a href="http://validator.w3.org/check?uri=referer">
<img height="31" alt="Valid XHTML 1.0 Transitional" src="http://www.w3.org/Icons/valid-xhtml10" width="88" />
</a>
</span><!-- End_Module_375 -->
</div></div>
</div>
</div>
</div>
<input name="ScrollTop" id="ScrollTop" type="hidden" />
<input name="__dnnVariable" id="__dnnVariable" type="hidden" />
<input type="hidden" name="__v13wstat3" value="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" /></form>
</body>
</html>