Turning directory browsing won't do a great deal to stop them from looking at each others scripts.... at least not if they were reasonably secure files which didn't let you look at the contents of config files directly.
Assuming the server is set to allow overrides you can just create a .htaccess file in the top level directory of your site (e.g. ~/public_html/.htaccess) and stuff apache directives in it. (e.g. Options Indexes).
The apache manual is good, http://httpd.apache.org/
and the httpd.conf file is well commented.