Do you keep local registry data when a user logs off? Sites are saved in the Windows registry, so you also need to save and restore the reg settings.
What you could do is create a default site, and then export it. This will result in a .ste file.
Then your users can simply import this site when they fire up Dreamweaver, so they get back all the settings.
Not as good as a predefined site, but definitely better than redefining it every time....