Due to the non-www stance some users use, I'm also going to describe how to send all www requests to the non-www domain... Be sure that you're not using both of these as you could cause a lot of looping on your webserver.
The instructions above are still valid, however, use this .htaccess block.
# Allow Re-Writing
RewriteEngine on
# Redirect WWW URLs to non-www
RewriteCond %{HTTP_HOST} ^www.corthell.net$
RewriteRule ^(.*) http://corthell.net/$1 [QSA,L,R=301]