I'm trying to install mod_perl and time and again have run into problems. 

Can anyone supply me with a from scratch set of instructions that will
get me up and running from a bare OS install of
Gentoo\Ubuntu\Fedora\Debian ?

A valid answer would consist of:

URLs for the versions of OS and the Apache releases of httpd and
mod_perl to be used
Any config options used during install of the OS
Complete set of commands and outputs used to install & configure
Apache and mod_Perl to a point where I can run a simple 'hello world'
script

I am listing out mod_perl installation steps for each os
1)Gentoo
this url will help you.
http://gentoo-wiki.com/Apache_Modules_mod_perl
2)Ubuntu
http://www.linuxforums.org/forum/ubuntu-help/68968-help-problem-compiling-apache-mod_perl.html
3)Debian
apt-get install libapache2-mod-perl2
4)Fedora
http://linux-sxs.org/internet_serving/apache2.html

All this urls consits of os version and step by step installation instructions

I missed out Debian url
http://www.debian-administration.org/articles/216