No one ( accept KM, but I think too much information sucks for newbies, so this node answers the question only )has addressed the fact that you want to set the environment variable... give the man what he wants!

$ENV{PERL5LIB} = '/foo';
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Notice that I didn't do this within BEGIN because you may also want to include other things like CGI.pm and that will break if you set the environment BEFORE you include your packages.

i_had_a_little_trouble_so_i_came_up_with_this