how do I disable margin displays?

[Brian Paul]

I recently upgraded to emacs 21.3.1 (included with Fedora Core 3).

I want to completely disable the margins displayed on the left and 
right edges of the window.

I've read this:

http://www.gnu.org/software/emacs/elisp-manual/html_chapter/elisp_38.html#SEC645

But I don't know how to implement this in my .emacs file.
The following doesn't work (for example):

(setq left-margin-width 0)

Thanks.

-Brian