serverpassword=lalalala is indeed the way to make this work, however, if you start the server by using the shortcut from your desktop (created during installation), the password is inoperative.
Change the "Start in" for the properties of the shortcut to "C:\Program Files\Teamspeak2\" if that was your installation folder. Not sure if this is a little bug, but in my case this "Start in" comment was empty, therefore it was creating a server.ini file and some others on my desktop.