Mayo, OS X is a unix multiuser OS, as the owner/admin you'll be able to set permissions for all files, folders, etc. even on volumes, external drives and removables...however, because of HFS+ formating they will lose those safeguards when booted in OS 9.
If you really want to lock down your 'puter, you could always use a firmware password. The machine will not boot from an external CD or drive, etc.
Encription and safe "shredding" is available for free using
Crypt, the only caveat is -- it's used from the command line.
As I have no need for such strong security, I have not tested Crypt.