If you open Multiple Users control panel, turn it on then create a new user. When you are creating the user, set type of user to "Panels". Now you can log in to that user, and Panels is used instead of the Finder.
By the way sometimes when using the Login Window to log in, you will get a beep and it will say Login Crashed unexpectedly, and logs into the default user. Nailed this crash down to "Apple Menu Options" control panel, if it's present it crashed, but I found a fix by replacing the control panel with one from Z1-9.2.2.