Sidebar:
<div id="sidebar" class="sidebar">
<!--Begin Sidebar Tabbed Menu-->
<script type="text/javascript">
var myTabs = new YAHOO.widget.TabView("tabspace");
</script>
<div id="tabspace" class="yui-navset">
<ul class="yui-nav">
<li class="selected"><a href="#tab1"><em>Populares</em></a></li>
<li><a href="#tab2"><em>Quentes</em></a></li>
<li><a href="#tab3"><em>Comentários</em></a></li>
<li><a href="#tab4"><em>Tags</em></a></li>
</ul>
<div class="yui-content">
<div class="tabs">
<ul><?php wp_list_cats('sort_column=name'); ?></ul>
</div>
<div class="tabs">
<ul><?php wp_get_archives('type=monthly'); ?></ul>
</div>
<div class="tabs">
<ul><?php wp_list_bookmarks('title_li=&categorize=0'); ?></ul>
</div>
<div class="tabs">
<ul><?php wp_list_bookmarks('title_li=&categorize=0'); ?></ul>
</div>
</div>
<!--End Sidebar Tabbed Menu-->
<ul>
<?php if ( !function_exists('dynamic_sidebar') || !dynamic_sidebar(2) ) : ?>
<?php endif; ?>
</ul>
</div>
CSS:
/*###### Tabs ###############################################*/
#tabspace {margin:0 0 10px 0 }
.tabs { clear:both;margin:10px 20px 0 0}
.tabs ul li {font-size:12px;list-style:none;border-bottom:1px dotted #cdcdcd;line-height:1.3em;padding:5px 0}
.tabs ul li a:hover {color:#000}
.yui-nav,.yui-nav li {list-style:none;margin:0;padding:0}
.yui-nav li a {text-decoration:none;color:#005288;display:block}
.yui-nav li.selected a {background:#e7e7da}
.yui-nav li a:hover {color:#FFF}
.yui-navset .yui-content{background:#e7e7da;border:1px solid #808080;border-top-color:#89897C;padding:.25em .5em}
.yui-navset .yui-content .yui-hidden{position:absolute;left:-999999px;visibility:hidden}
.yui-navset li em{font-style:normal}
.yui-navset{position:relative;zoom:1}
.yui-navset .yui-content,.yui-navset .yui-content div{zoom:1}
.yui-navset .yui-content:after{content:'';display:block;clear:both;color:#FFF}
.yui-navset .yui-nav{border:solid #89897C;border-width:0 0 2px;overflow:hidden;zoom:1}
.yui-navset .yui-nav a{background:#e7e7da;border:solid #808080;border-width:0 1px;color:#89897C;position:relative;text-decoration:none}
.yui-navset .yui-nav li{margin:0 .16em 0 0;display:inline-block;display:-moz-inline-stack;*display:inline;vertical-align:bottom;cursor:pointer;zoom:1}
.yui-navset .yui-nav li a{display:block;display:inline-block;vertical-align:bottom;zoom:1}
.yui-navset .yui-nav li a em{display:block}
.yui-navset .yui-nav a em{font-size:12px;border:solid #808080;border-width:1px 0 0;cursor:hand;padding:.25em .75em;left:0;right:0;bottom:0;top:0;position:relative;font-weight:bold}
.yui-navset .yui-nav .selected a,.yui-navset .yui-nav .selected a:focus,.yui-navset .yui-nav .selected a:hover{background:#89897C;color:#FFF}
.yui-navset .yui-nav a:hover,.yui-navset .yui-nav a:focus{background:#89897C;color:#FFF;outline:0}
.yui-navset .yui-nav .selected a,.yui-navset .yui-nav .selected a em{border-color:#89897C;color:#FFF}
Foi apenas desde que adicionei a parte das tabs.