in reply to
Introductory books about Perl and mod_perl
Liz already pointed you out to my "Where and how" node. A lot of good tutorials can be found here at Perl Monks.
Before you, several people have asked for the best place or the best way to start learning Perl and others have answered: here, here, here and here.
With regards to mod_perl, you'd best go to the source, which is http://perl.apache.org.
Or use (one of) these books:
Practical Mod_perl by Stas Bekman, Eric Cholet
( Chapter 6: Coding with mod_perl in Mind can be read online).
mod_perl Developer's Cookbook by Geoffrey Young, Paul Lindner, Randy Kobes
( 3 introductions and chapters 1, 3, 4, 7, 13, 16, Appendix B can be read online).
A bit of search in the Monks or a Google search sweep lists dozens of interesting places. Take your pick.