Depends on what you are really asking.  Do you mean from an administrative perspective you only want the module visible to users that are logged in?  If that is the case, restrict the "View" rights to only be visible to "Registered Users". 

If this is not what you are asking, then let me pose a different question.  Do you mean the module itself needs to be aware if the user is logged in or not?  If that is the case, do you control the code for the module itself?  If you don't, then not much you can do besides ask the developer to add the check himself.  If you do control the code, then simply check for "this.UserId > 0".  Assuming true, then the user is logged in.  Assuming false, then the user is not logged in.

Doh!  You're right although I don't think it would ever be possible for UserId to be 0 since default accounts even start numbering at 1 (host) and 2 (admin).