This part that needs to go in the head section in header.php:

<script>
// Function to view tab
function viewTab(tabId) {
	// Get all child elements of contents-container
	var elements = $(contents-container).childElements();
	// Loop through them all
	for (var i=0, end=elements.length; i<end; i++) {
		// Is clicked tab
		if (tabId == elements[i].id) {
			// - Show element
			elements[i].show();
			// - Make sure css is correct for tab
			$(tab-+ elements[i].id).addClassName(active-tab);
		}
		// Is not the clicked tab
		else {
			// - Hide
			elements[i].hide();
			// - Make sure css is correct for tab
			$(tab-+ elements[i].id).removeClassName(active-tab);
		}
	}
}
</script>




The register part that goes in functions.php:

if ( function_exists(register_sidebar) )
	register_sidebar(array(name=>Recent Posts));
	register_sidebar(array(name=>Popular Posts));
	register_sidebar(array(name=>Recent Comments));
	));




The Tabbed box:

<ul id=tabs>
	<li id=tab-content-recent class=active-tab>
		<a href=javascript:viewTab(content-recent);>Recent</a>
	</li>
	<li id=tab-content-popular>
		<a href=javascript:viewTab(content-popular);>Popular</a>
	</li>
	<li id=tab-content-comments>
		<a href=javascript:viewTab(content-comments);>Comments</a>
	</li>
</ul>
<div id=contents-container>
	<div id=content-recent>
		<! Recent tab widget area >
		<?php if ( !function_exists(dynamic_sidebar) || !dynamic_sidebar(Recent Posts) ) : ?><?php endif; ?>
	</div>
	<div id=content-popular style=display: none;>
		<! Popular tab widget area >
		<?php if ( !function_exists(dynamic_sidebar) || !dynamic_sidebar(Popular Posts) ) : ?><?php endif; ?>
	</div>
	<div id=content-comments style=display: none;>
		<! Comments tab widget area >
		<?php if ( !function_exists(dynamic_sidebar) || !dynamic_sidebar(Recent Comments) ) : ?><?php endif; ?>
	</div>
</div>