By default, each user in Interspire Email Marketer can only see the contact lists and contacts that belong to them. If they can see each others lists and contacts, it means you've accidently given the users the wrong permissions.
In the User Settings options under the section called ' Contact List Access Permissions' you can specify what access to give different users.
Simply set the option to 'Users own lists plus the following' and then if you like you can also select additional lists they have access to.
