I found some comments in this thread (http://www.jivesoftware.com/community/message/50447#50447) that clarify that guest access is enabled by default in Clearspace X but not in Clearspace.
How can I enable guest access in Clearspace?
I tried giving "anyone" read access but (at least the 1.4 eval version I'm testing with) always forces me to log on as a registered user.
In the future, would you post non-developer related questions here: http://www.jivesoftware.com/jive/index.jspa
To answer your question, just add the following Jive Property in the admin console: