[CentOS] User creation problem

system-config-users  is giving me a problem.  I need to create a user 
called 'groupware', without a home directory, and belonging only to a 
non-privileged group.  I can create the user, but it sets it to belong to the 
group 'users'.  When I try to set its default to 'nobody' and delete 
the 'users' entry it tells me that I must enter a home directory.

How can I get around this?

Anne