You need to set the permissions of the subsite to not inherit from the parent. This is an option when you create the site. To stop inheriting permissions on an existing site, go to:
Site Actions -> Site Settings -> Advanced Permissions -> Actions -> Edit Permissions
Then you can set who has access to the subsite. A user with no permissions in the subsite will not see the tab.
It's all explained here.
Andrew Strong
2009-08-11 22:15:17