While most people would not consider it wise to do so, you can open up chats to guest access (providing you allow people to login as a guest to the site in which the chat is housed). Do to so, once logged in as an admin, click Users-->Permissions-->Define Roles. Click on Guest to go to that role. Click Edit at the top of the page. Scroll down to Chat and, by Access a Chat Room, change the setting to Allow (second column on my interface). Scroll down to the bottom and click Save Changes. Walla! Guests can now access chat rooms. Just remember, guest activity can't ve tracked very well so, if you have unscrupulous types access your site, they could
spam a chat room or any other place where they can enter text (i.e. wikis, blogs, etc).