In W2K Pro, I used to just create a group called "No Access Lock" or something like it and use folder permissions to toggle whether the folder was available or not.  A user would then need Admin privileges to change the file/folder permissions to make it accessible again.  It was a lightweight way to control the accessibility of a folder.  Unfortunately it doesn't work the same way in WinXP Pro and I've been unable to figure out a way to do it (with permissions).  I think I'll give WinGuard a shot.