When you go to join the new GEC, you will first need to be logged into a Google account. From there, only the first time that you join the GEC, you should follow the instructions I just posted on this thread. Click "Join Group" and then select "Import" to connect your GEC username/posting history with your Google account. 

Note: By making this connection, you are simply claiming ownership of your old content. Your GEC content is still anonymous. However, once you join the GEC, you will see a My Membership tab. In this tab, you can control your E-mail preferences for the GEC, and you also have an option to "Link to My Google Profile." If you check this option, your Google profile will be linked to from your GEC form member profile.

Mark