You should have received an email from Plimus with a link to to download the game. Registration codes are no longer used. See the post at
http://www.ldwforums.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=233323#Post233323 for more details.
If you can't see that an email has been received, check your spam folder.
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To err is human; to arr is pirate.