Hi Hank,
Actually, the Drop Box is set up just the way you need it from the
factory. If you allow persons to access your computer, they will
have "Read" access to the Public folder in your Home directory and
"Write/Drop Box" access to the Drop Box in that Public folder. Then
navigate to the bottom of the Info window and press VO keys+space on
the Details item to expand it. You will then be able to read the
existing privileges. There is a unlabeled button you can press to
unlock the existing privileges and make modifications. I do caution
you though to be very careful when modifying privileges/permissions
on things as you can cause yourself huge grief if you don't know what
you're doing.
Later...
You can modify privileges by selecting the folder you wish to set
privileges on, then pressing cmd+i to get the "Get Info" window.
Tim Kilburn
& Carter the Canine
Fort McMurray, AB Canada