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.
Although I have a high-end system and don't really have any issues with framerate I still noticed higher framerates after install. On an older system there's a chance that you already have this installed and won't see any improvement, but it's worth a shot imo.