[davidw]

Find this in your navbar template:

<if condition="$show['popups']">
<!-- NAVBAR POPUP MENUS -->

	<if condition="$show['searchbuttons']">
	<!-- header quick search form -->
	<div class="vbmenu_popup" id="navbar_search_menu" style="display:none" align="$stylevar[left]">
		<table cellpadding="4" cellspacing="1" border="0">

Add after:

<tr>
	<form action="{$vboptions['google_forum_path']}" id="cse-search-box" target="_top"><td class="thead">Search Site / Google</td>
</tr>
<tr>
	<td class="vbmenu_option" title="nohilite">
		<table border="0">
			<tr>
				<td nowrap="nowrap">
					<div>
						<input type="hidden" name="cx" value="{$vboptions['google_pub']}" />
						<input type="hidden" name="cof" value="FORID:9" />
						<input type="text" name="q" size="{$vboptions['google_box_width_nav']}" />
						<input type="submit" name="sa" value="Go" />
					</div>
				</td>
			</tr>
		</table>
	</td></form><script type="text/javascript" src="http://www.google.com/coop/cse/brand?form=cse-search-box&amp;lang=en"></script>
</tr>

Save and reload.