So this is correct:

    (setq desktop-enable t)
    

This is probably not correct, since setting a variable will not load
a file.  *Customizing* this variable will store extra information in
the .emacs file which will then load desktop.el.  But for the
non-custom solution, I think the best thing would be

(desktop-mode 1)

And desktop-mode is an autoloaded global minor mode from desktop.el
which also sets desktop-enable to t when active.

Alex.