You have to separately register for the game itself. So your forum account will NOT work in-game.
Steps:
1. Register a new in-game account.
2. Click the e-mail activation link.
3. Activate account every once in a while.
1.
http://app.eurobattle.net/register < This is where you can register a new in-game account.
2. You will then have to click the activation link in your e-mail.
3.
http://app.eurobattle.net/activate/step2 < This is where you can activate it. You'll have to activate it every once in a while.
I hope this helped.