google for subdomains and account keys: http://cleanair.highgroove.com/articles/2006/08/14/simplied-subdomain-authentication-in-ruby-on-rails http://wiki.rubyonrails.com/rails/pages/HowToUseSubdomainsAsAccountKeys
http://dev.rubyonrails.org/svn/rails/plugins/account_location/README
What you need to do if you want to host the same application on two domain names, is put a ServerAlias in the Apache config file. That way, both (or more than two) domain names will point to the same application.
http://httpd.apache.org/docs/1.3/mod/core.html#serveralias
Best regards
Peter De Berdt
Chances are that the add-on domain option in cpanel actually adds this line to the apache config file.
You might also want to look at any options on there concerning “mirroring”. I’m currently using such a setup to serve multiple sites out of one app.
RSL