Is your layout a fixed width or it is liquid? Don't use the same "id" twice in one page. Personally, I think you're over DIV your layout.
Here's my code based on your layout.
<style type="text/css" media="screen">
/* Header and Menu */
#brdheader {
width: 100%;
margin: 0 auto;
margin-left: 150;
margin-right: 150px;
margin-bottom: 30px;
background: red;
}
#brdheader h1 {
}
#brdheader ul {
}
#brdheader ul li {
}
/* Content and Sidebar */
#contentwrapper {
width: 100%;
margin: 0 auto;
margin-left: 150px;
margin-right: 150px;
margin-bottom: 30px;
}
#sidebar { /* Fixed Width */
width: 250px;
float: right;
height: 300px;
background: red;
}
.blocktable { /* Liquid */
margin-right: 260px;
height: 300px;
background: red;
}
#brdstats, #brdfooter {
width: 100%;
margin: 0 auto;
margin-left: 150px;
margin-right: 150px;
margin-bottom: 30px;
background: red;
}
</style>
<div id="punwrap">
<div id="pun<pun_page>" class="pun">
<!-- Header and Main Menu -->
<div id="brdheader" class="block">
<div class="box">
<!-- Header -->
<div id="brdtitle" class="inbox">
<pun_title>
<pun_desc>
</div>
<!-- Menu -->
<pun_navlinks>
<!-- Forum Status -->
<pun_status>
</div>
</div>
<!-- Content and Sidebar -->
<div id="contentwrapper">
<!-- Sidebar -->
<div id="sidebar">
This is the sidebar
</div>
<!-- Forum Content -->
<pun_main>
</div>
<!-- Forum Stats and Footer -->
<pun_footer>
</div>
</div>