Adding to @INC

I just installed Mac OS X 10.5, and I'm trying to get Perl back up to  
snuff. My current @INC contains only
   /System/Library/Perl/5.8.8/darwin-thread-multi-2level
   /System/Library/Perl/5.8.8
   /Library/Perl/5.8.8/darwin-thread-multi-2level
   /Library/Perl/5.8.8
   /Library/Perl
   /Network/Library/Perl/5.8.8/darwin-thread-multi-2level
   /Network/Library/Perl/5.8.8 /Network/Library/Perl
   /System/Library/Perl/Extras/5.8.8/darwin-thread-multi-2level
   /System/Library/Perl/Extras/5.8.8 /Library/Perl/5.8.6
   /Library/Perl/5.8.1/darwin-thread-multi-2level
   /Library/Perl/5.8.1

I plan to use CPANPLUS to install new packages and modules. Right now  
it installs them in
   /opt/local/lib/perl5/site_perl/5.8.8
This seems like a good place, but how can I add this directory to  
@INC? I would prefer not having to start every script with
   use lib '/opt/local/lib/perl5/site_perl/5.8.8';

Thanks for your help.

Vic Norton