Ubuntu :: How To Set Default Window Manager

I have a pretty vanilla install of Ubuntu Lucid. I would like to change my default WM to sawfish. I have it installed, and it works routinely, I would just like to have it start automatically on log-in, rather than Lucid. A few sources have suggested that the way to do this is during log-in. They refer to a "session" I could choose, which would allow me to set the WM. I remember doing this in the past, but can't find such an option on the login page, now.

I have also experimented with changing .gconf/desktop/gnome/applications/window_manager/ using both gconf-editor and emacs. However, when I change "/usr/bin/compiz" to "/usr/bin/sawfish", log out, and log back in, I find that compiz starts anyway, and the setting in that file has been restored to compiz. Clearly, the gconf mechanism is getting the information from some other source.