Device::ParallelPort

Available on CPAN, and lets you talk to the parallel port (on Windows too!)

use strict;
use Device::ParallelPort;

$port = Device::ParallelPort->new;

$port->set_bit( 1, 1 ); # now it's on
$port->set_bit( 1, 0 ); # now it's off

Note: You must be root or have rootlike mojo (sudo, setuid, whatnot) for this to work.