deny from all

Google has a guide, for Google
_ http://www.google.com/support/webmasters/bin/answer.py?hl=en&answer=164734

Table of HTTP status codes
_ http://www.google.com/support/webmasters/bin/answer.py?hl=en&answer=40132

Nice explanation of the error codes
_ http://diveintomark.org/archives/2003/03/27/http_error_410_gone

Apache / .htaccess specific
_ http://www.javascriptkit.com/howto/htaccess14.shtml
_ http://www.kavoir.com/2009/01/htaccess-deny-from-all-restrict-directory-access.html
_ http://www.askapache.com/htaccess/using-http-headers-with-htaccess.html

About robots, useless
_ http://www.robotstxt.org/