I have the Eagle book (aka Writing Apache Modules with Perl and C). It's quite good and has really nice examples. You can ofcourse also check the mod_perl site. I recommend using a 1.3.x release of Apache since you'll probably find more people using it and being able to help you.

The best way for me to learn about mod_perl was by experimenting and using the perl skills I already had. mod_perl isn't a good way to learn perl IMHO so you better work on a good base (if you don't have it yet). Don't be afraid to take a random Apache:: module and read through the source code...

Greetz
Beatnik
... I'm belgian but I don't play one on TV.