MySQL: The home page for MySQL, described by its authors as a “mostly free” database, is at http://www.mysql.com/. That site will lead you to pages from which you can download the latest version of MySQL, read documentation and FAQs and subscribe to MySQL-related mailing lists.
Perl: The Perl home page at http://www.perl.com/ contains a wealth of links to Perl-related resources. If you need to download the latest version of Perl or any module, this is a good place to start.
DBI: The Perl Database Interface (DBI) libraries are available from CPAN. You will have to download and install not only the overall DBI library, but also the DBD for your particular database.
Finally, Jakob Nielsen's web site on usability, at http://www.useit.com/, is an outstanding source of information. His essay on searching, which I mentioned in this article, is at http://www.useit.com/alertbox/9707b.html.