Enable CGI, SSI with .htaccess:
http://www.besthostratings.com/articles/enable-cgi-php-ssi-htaccess.html∞


Internal server error (Plesk )
http://kb.swsoft.com/en/430∞
http://www.brandonchecketts.com/archives/quick-perl-internal-server-error-http-500-fix∞

SerevrsideIncludes (SSI)

Disable TRACE method (apache security!)
http://www.ducea.com/2007/10/22/apache-tips-disable-the-http-trace-method/∞

All about .htaccess file:
http://www.wiscocomputing.com/articles/using_htaccess.htm∞
http://www.hybrid6.com/webgeek/2006/12/htaccess-ip-banning-block-bad-visitors.php∞

Prevent httpd DDOS attack:
iptables -I INPUT -p tcp --dport 80 -i eth0 -m state --state NEW -m recent --set iptables -I INPUT -p tcp --dport 80 -i eth0 -m state --state NEW -m recent --update --seconds 60 --hitcount 5 -j DROP

Howto use cpanel include file for custom changes to vhosts:
http://www.jangro.com/a/2007/11/23/cpanel-easyapache-and-customizing-httpdconf/∞