The only problem with the DBI book is that it is mostly just a repeat of DBI.pm's POD. I bought it, am glad i bought it, but i rarely use it. Likewise, by the time a good CGI is out, it's already outdated -- these days, everyone seems to be shifting to templates anyways (and the one good looking book on the subject appears to still not be released).

I recommend you instead spend your money on either Data Munging with Perl and/or Network Programming with Perl. Even though these two books are a far cry from focusing on CGI and database programming, i strongly feel they are the next step you need to take. If you can only afford one, get the Network book -- there is a lot of good history you may have missed that will help strengthen your foundation.

UPDATE:
I missed this question: "Is DBI how perl talks to MySQL?"
Yes and no. To be just a bit more technical, DBI is how Perl "talks" to a data store, which could be a Relational Database Management System (MySQL, PostgreSQL, etc.) or a plain CSV file, XML file, Berkely database, etc. DBD::mysql is how Perl "talks" to MySQL.

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)