You don't have Ubuntu 9 because there isn't a version 9. You might have Ubuntu 9.04 or Ubuntu 9.10 though.
By disk do you mean directory? As in "How can I allow all users to read and write to a directory but not be able to delete each other's files, like how /tmp works?" If so then answer is to set the sticky bit
Code:
$ chmod +t directory
$ chmod a+rwx directory
Or
Code:
$ chmod 1777 directory
