If you are signing into the LEGO Universe client, it does not matter if you have an account on this website or at LEGO.com. You need to make sure in your client’s boot.cfg file that your AUTHSERVERIP is connecting you to a server that is running. Since there are no public servers online at the moment, I recommend you use
AUTHSERVERIP=0:localhost, with a server that is easy to set up, like 0.5.1. Just download it, extract it, and run the .exe file inside before you launch the client.