Why doesn't the Security Tab appear?

I'm certain that I'll feel dumb after getting the answer to this, but here goes...

On WindowsXP Pro, SP2: Why is it that only on one of the three machines sitting in front of me, do I see a "Security" tab when right-cliking a folder and the other two only show me a 'Sharing' tab??

My requirement: I have to grant specific users some specific rights inside the file-system. Using the 'sharing' tab, I open up access full-blast to everyone logged into the system. If I had the good ole' Security tab, I can pick which users get what privs, to what file. This is what I need. --Why do I have a Sharing tab and not a Security tab?

 

SOLUTION: Tools | Folder Options.. Un-check "Use Simple File Sharing ".

Once this is un-checked, the Sharing... tab becomes a Security... tab, and all the granular privs are there.

 

Furthermore, if you have any computers running XP Home, the security tab is only available in Safe Mode while logged in with Administrator privileges.