More and more rooms are being set permanently to "registered users only" mode. This is quite sad.
In order to register a nickname, simply go to the site, or enter any room, with a nickname you intend to register. Click the status bar, and type "/msg nickserv register password email" (without the " "s) as it shows in the video below, where "password" is whatever the hell you wish it to be, and "email" is a working email. It has to be a working email; otherwise you won't be able to enter the confirmation code, derp.
Once confirmed, I suggest you type "/msg nickserv set enforce ON" to prevent anyone from using it when you're not online; as before, type this in the status bar.
Whenever you go into ICQ from that point forwards you will type "/msg nickserv identify password" and this will log you in. You may now speak freely on +r mode rooms (which are increasing in number swiftly.)