Don't follow any instruction for WordPress installation that is that old. Menus have changed, terms have changed.
I couldn't figure out that ottopress instruction, had to work it out and document what worked, even correcting the mis-tries I had done.
http://lcblog.lernerconsult.com/2012-wordpress-3-multi-site-domain-mapping/
You may have to change some of the WordPress installation too, especially if you didn't install WordPress in the root of your account or the root of a subdomain -- domain mapping (and likely much more of multi-site) will not work installed in a folder.