It is not a good idea to require registration in order to download the game. To post on the forum, maybe, but the download itself should be accessible without jumping through hoops. This will annoy people who have been following the production of TSL but are not members of the forum.
Also, despite your request for people not to redistribute TSL, human nature means that people will disregard that and redistribute it anyway, especially since it's free. By requiring registration, you will drive people away from the official site and towards the unofficial mirrors.