Programmatically setting the frame size and position

[Davin Pearson <davin.pearson@gmail.com>]

I would like to know how you go about setting the
size and position of a given frame using Elisp instead
of the mouse.

I am interested in using the speedbar.el but it currently
appears in a maximised state.

I don't want to use the mouse to resize and reposition 
the frames so that they sit beside each other every
time I start speedbar.el

Here is the Elisp code that I have written (based on the built in
Emacs manual) but doesn't work. 

(progn
   (setq fc (current-frame-configuration))
   (setq w (assq 'width (cadadr fc))
   (setcdr w 20)
   (set-frame-configuration fc))

What code do I need to write to get it to work?

Please advise me as I am stuck at the moment.