User and share administration is performed for the time being directly through the Samba Server Configuration panel. (In the future this functionality will be controlled through the setup area in your HDA.)
To get there, you have to be at the desktop of your HDA (either directly or through [[VNC]]), and go to System -> Administration -> Samba. Note: it may be under System -> Administration -> Server Settings -> Samba, if you have more server services installed.
Here is what it looks like in my case.