I am using IP 2007 so steps may be different but to set up user roles go to Tools > User roles.
Add User role by entering individual user names (from Active directory, Ex: dns\username), by group, or a name from the form.
In your control properties under conditional formatting (in 2007 its on Display tab), add a condition if "User's current role" equals (or is not equal to) <role you created>, do something (hide, disable format font, line etc etc)