Adding a rails app to a subdomain

I'm trying to add a separate rails app to my existing rails app
running on apache.

I followed the steps at this site (http://blog.codahale.com/2006/06/19/
time-for-a-grown-up-server-rails-mongrel-apache-capistrano-and-you/)

so my setup looks like this

/etc/apache2/http.conf

NameVirtualHost *:80

<Proxy *>
  Order allow,deny
  Allow from all
</Proxy>

#gawkk main site
Include /etc/apache2/conf.d/gawkk/gawkk.conf
Include /etc/apache2/conf.d/gawkk/gawkk.cluster.conf

#blog
Include /etc/apache2/conf.d/blog/blog.conf
Include /etc/apache2/conf.d/blog/blog.cluster.conf

each of the sites have their own common file(i'm not sure if that's
the way it was suppose to be or not)

in the common file they have

  ServerName blog.myapp.comm
  DocumentRoot /var/www/blog/current/public

  RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_FILENAME} !-f
  RewriteRule ^/(.*)$ balancer://blog_cluster%{REQUEST_URI} [P,QSA,L]

  ServerName www.myapp.comm
  DocumentRoot /var/www/myapp/current/public

  RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_FILENAME} !-f
  RewriteRule ^/(.*)$ balancer://myapp_cluster%{REQUEST_URI} [P,QSA,L]

depending on which site i put first in the http.conf that cluster
pulls all the requests.

I can't seem to find a way to separate the domain and subdomain apart
so that each cluster pulls the request.

Any help would be MUCH appreciated!