Mac OS X Unix based permissions are simple and effective, but sometimes you may need more flexibility. For example, you may need to manage several groups of users and set permissions for multiple groups in one single folder. In Mac OS X you can use Access Control Lists (ACL) to set advanced permissions to use with DF files and folders.

You can find further info about ACL in these links:
http://arstechnica.com/apple/reviews/2005/04/macosx-10-4.ars/8
http://www.makemacwork.com/control-file-access-with-acls.htm

By default Mac OS X hides all the system folders. If you need to add one of these folders to Dynamic Folders you have first to configure Finder to let you see them. To do this open Mac OS X Terminall.app and type the following commands:

defaults write com.apple.Finder AppleShowAllFiles YES
killall Finder

Now you should see all the files on your system including the hidden ones. If you want to revert this and hide system folders, type the following commands at Terminal.app

defaults write com.apple.Finder AppleShowAllFiles OFF
killall Finder