You must have fixed this or changed your theme because I no longer see the problem you describe.
All of the files that affect your site's style should be in your Geeklog theme and in your phpBB theme. Since the phpBB interface is wrapped in the Geeklog header and footer, your Geeklog theme will often affect your phpBB look and feel. When doing major theme changes, you will likely have to edit files in both locations.