Mount the share on the client machines. Drag the share to Log in Items in Accounts prefs on the client machines.

You'll need to use SMB sharing for the Win boxes, they won't do AFP, they can't understand the HFS file system.

Here's some other stuff on sharing with OS X and Windows that may save a few hairs.

Snow Leopard Server and Win sharing leaves a lot to be desired, I think I warned you already. Tiger worked so much better.