In phpGroupWare it is very easy to maintain User Accounts. You can easily add , remove or set previleges to the user accordingly.
To create a user account goto User Accounts section of Administration and the click the Add button. Now a form would be displayed. FIXME : should i explain the process :-). After submiting the form you would be sent back to the accounts page and you can now see the new user you have just created. Isn't it easy !!!