If you're a book fiend like me, you can start out with Learning Perl, from O'Reilly. It is endearingly known as the Llama book.

Once you've digested that, CGI Programming with Perl, also from O'Reilly, is a pretty good introduction to CGI, and devotes a chapter to mod_perl. (This one is known as the Mouse book. Be sure to get the 2nd edition. The first is quite different and doesn't discuss mod_perl at all.

With those introductory books out of the way, no home should be without the Camel book (Programming Perl from O'Reilly. And you can dive into mod_perl in greater depth with mod_perl, also from O'Reilly.

The latter is the only book out of the four mentioned that I don't have. But as one who does have the Camel book, the Llama book, the Owls book (Mastering Regular Expressions), the Mouse book (1st and 2nd ed.), the Ram book (Perl Cookbook), the Panther book (Advanced Perl Programming), the Koala book (HTML), the Groundhog book (Perl for System Administration), and the Rhino book (Javascript), I can say that for the most part, O'Reilly & Assoc. books are top quality.

The recommendations for online learning resources are also very much on track. You can learn an awful lot just by reading online tutorials, Apache's mod_perl documentation, and the Perl POD pages. I find that a four-pronged approach works best for me: 1. The perldocs. 2. The books. 3. The web (including Perlmonks). 4. Experimentation and practice.

Good luck, and enjoy.