Try adding this to your ~/.profile
export PERL5LIB=${PERL5LIB}:/opt/local/lib/perl5/site_perl/5.8.8
OS X 10.5 (or at least my version of 10.5) uses ~/.bash_profile not
~/.profile for user overrides to the default profile (/etc/bashrc).
If this is a multiuser machine and you want the other users to see the
modules as well you can set it in the default profile instead of your
own.
I think either ~/.profile or ~/.bash_profile will work. My ~/.profile
was created by a previous fink installation if i remember correctly.