Actually, to follow the book you don't even need mod_perl. The scripts in the book are ordinary CGI scripts - mod_perl handlers are not used. mod_perl (via Apache::REgistry) is only recommended by DuBois for improved performance.

However, if you really wan't to use mod_perl, you can download one of the bundles other monks have suggested, or get one from apache.org - where you can get perl 5.6.1 + Apache 1.3.27 + mod_perl-1.27 OR Perl 5.8.4 + Apache 2.0.50 + mod_perl-1.99. Both distributions come with Apache::Session and DBI/DBD::mysql