Hi Chris,
Hiding a Community or Collection is possible in DSpace 7 in the same manner as in DSpace 6. You just need to be aware of how DSpace permissions work. In DSpace, permissions are managed object by object, with only a few exceptions.
Step 1: To Hide a Community/Collection, first you MUST change its "READ" permission. This can be done from the Edit screen, "Authorizations" tab. You want to change the "READ" action to a group which is *not* Anonymous (e.g. "Administrator"). At this point, you've only hidden the Community or Collection object itself, and not everything within it.
At this point, you've hidden The Community/Collection and all the Items *currently* within it. The only thing to be aware of is that Items which are added in the future to this Community/Collection *might* default to having public permissions. You can change this though by Editing the Collection and on the "Assign Roles" tab, changing the "Default item read access" setting to restrict future Items to a specific group. This setting defines which group in DSpace will get "READ" access to items submitted to this Collection in the future.
In the future, if you ever want to make these Communities/Collections public again, you'd undo these three steps...and set all the permissions back to "Anonymous" group (which gives everyone access to the objects).
Hopefully that helps, but let us know if it's still confusing.
Tim