Gina,
It appears he is using the username 'Admin' for his workstation logon, which is hardcoded into VSS for admin rights. You basically have two options:
1) Have his network (workstation) login username changed to something other than 'Admin', or
2) Log in to VSS admin, click (select) the admin user, click on Tools, then Options, under the General tab the second check box down (VSS 5.0) is 'Use network name for automatic user log in', uncheck this box. This would require all VSS users to enter a username and password each time they wanted access.
Preferably, it would be most convenient if you could get your network administator to disallow 'Admin' as a workstation login, since it is hardcoded in VSS.
Jerry