Mac Mini Server Sharing Alias

Mac Mini Server (Snow Leopard)

I modified my share points to share files from my external hard drive.

What I want to be able to do is to automatically copy anything (for example, newly created users) onto my hard drive.

I've tried to use alias but that does not work. Help?

Computer hard drive is MacintoshHD
External hard drive is FileServerHD

I'm sharing the FileServerHD

I want to be able to create new users on MacintoshHD and have them automatically stored on FileServerHD without overwriting the data from the other users