self explanatory.. I've always wondered about this.
anybody know if I can do this?
For network access or local user?
For a local user I would create a password protected disk image ( *.dmg file) with Disk Utility . Works well. Looks like a file, but is really usable like a removable disk or folder. You can also set permissions for access via the Info box for the folder, though it has limitations as to the amount of access you can deny.
For network sharing security sharing is available under the "Sharing" icon of system preferences.