Peer-to-peer networking can be very easy with Mac OS X. But due to an issue with ACLs it can be a little annoying in the Leopard release of Mac OS X. Essentially, when files are copied to the drop box, they aren’t accessible by the owner of the drop box due to an ACL issue. To repair, run this command, replacing short_name with the username that has the dropbox:
chmod +a "short_name allow list,add_file,search,delete,add_subdirectory,delete_child,readattr,writeattr,readextattr,writeextattr,readsecurity,writesecurity,chown,file_inherit,directory_inherit" /Users/short_username/Public/Drop Box