Must being having a brain fart, because I can't remember how to only share my Public > Drop Box...right now you can get to pretty much anything on my machine from another computer.
Unless you changed it permissions, people on your network can put files in, but not take them out. Remember on any object/folder you can do a get info on it and changed it's properties. Also, if you want to share certain stuff, the best option is a program (that acts like a System Preference) called SharePoints that will greatly help in sharing specific folders, etc.