Which version of mod_perl are you going to use? O'Reilley's Practical Mod_Perl is great for mod_perl 1.x but only touches upon mod_perl 2. A lot of things have changed since the book came out and initially I had trouble making even the basic examples work (especially ones involving Response Handlers). Fortunately the documentation on perl.apache.org is superb and even has a migration guide to mod_perl2: http://perl.apache.org/docs/2.0/user/porting/compat.html