You see by default OSX only allows you to share your home folder which is lame [Actually you can do more then that , its just that - its not bulit into the GUI. You'll have to do it by hand]

But fortunately , there is a GUI/Front-end tool that allows you to configure 'Share Points' aka enable sharing on disks , folders and stuff like that. Instead of sharing the home folder alone , now you can share an external HD , or an iPod across the network

Heres the tool

www.hornware.com/sharepoints/