Use Your Gamer Launch Account
Your account from any Gamer Launch site is valid here.
If you already have a Gamer Launch account connect your Facebook account on your user profile first before using Facebook connect to login. Otherwise you may end up with a new account.
Fun game, you can login with a steam acct and get a copy. Giveaway ends in a couple days. I dunno how the giveaway actually works though... so good luck!