That is a core file. Don’t hack that. I’m going to assume you’re using the parent/chid theme that comes with BP 1.1.3. If so, copy the following file into your child theme (including the folders… i.e. /directories/groups/):
You can find the sidebar area there pretty easily:
<div id="sidebar" class="directory-sidebar">
Simply code what you want right inside that div. Or to make it use one of the existing three sidebar in the classic theme, add this code:
<?php if ( !function_exists('dynamic_sidebar') || !dynamic_sidebar('third-section') ) : ?>
This would add the widgets from the “third-section” sidebar in Appearance > Widgets.
You could also register a new sidebar if you wish, just for groups. Create a functions.php file in your child (if you’re using a child theme) and add this:
'name' => 'groups-sidebar',
'before_widget' => '<div id="%1$s" class="widget %2$s">',
'after_widget' => '</div>',
'before_title' => '<h2 class="widgettitle">',
'after_title' => '</h2>'
In that case… just change “third-sectoin” in the code above to “groups-sidebar”… or whatever you choose to name that widget area when you registered it using the “register_sidebars” function above.