You have a couple of options;
one, if you are unix competent, you can manually edit the /etc/smb.conf file and enable Windows File Sharing in the Sharing tab is System Preferences.
two, you can use a tool called SharePoints (
http://www.hornware.com/sharepoints/) to create the entry's for you. I suggest this option as it is best for most users and you are far less likely to mess things up if you aren't familiar with samba. Also SharePoints allows you to configure AFS shares as well.