The advantage of using apache (or nginx) as a proxy is that it can load-balance between different mongrel (or thin) instances. So you would have to start three mongrel instances (services) and configure apache to proxy those.
Configuring apache to different mongrel processes is pretty straightforward, can be found all over the internet. Here is an example of a httpd-vhosts.conf (replace yourapplication by your actual application/domain and root-folder):
<VirtualHost *:80>
#ServerName 10.200.65.35
#ServerAlias 10.200.65.35
ServerName yourapplication.com
DocumentRoot d:/yourapplication/current/
<Directory c:/yourapplication/current/public/ >
Options Indexes FollowSymLinks MultiViews
AllowOverride All
Order allow,deny
allow from all
</Directory>
# On active les proxy qui sont par défaut désactivés
<Proxy *>
Order allow,deny
Allow from all
</Proxy>
<Proxy balancer://mongrel_cluster>
BalancerMember http://127.0.0.1:4000
BalancerMember http://127.0.0.1:4001
BalancerMember http://127.0.0.1:4002
</Proxy>
ProxyPass / Balancer://mongrel_cluster/
ProxyPassReverse / balancer://mongrel_cluster/
#ProxyReserveHost on
#log files
ErrorLog "/Program Files/Apache Software Foundation/Apache2.2/logs/yourapplication_error.log"
# Possible values include: debug, info, notice, warn, error, crit,
# alert, emerg.
LogLevel warn
CustomLog "/Program Files/Apache Software Foundation/Apache2.2/logs/yourapplication_access.log" combined
#Rewrite stuff
RewriteEngine On
# Rewrite index to check for static
RewriteRule ^/$ /index.html [QSA]
# Rewrite to check for Rails cached page
RewriteRule ^([^.]+)$ $1.html [QSA]
# Redirect all non-static requests to cluster
RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_FILENAME} !-f
RewriteRule ^/(.*)$ balancer://mongrel_cluster%{REQUEST_URI} [P,QSA,L]
</VirtualHost>
Another, very promising alternative to deploy on windows is using TorqueBox.
TorqueBox is JBoss/Jruby based solution, and thus platform independent. In benchmarks it is shown that TorqueBox performs incredibly well, and actually anybody should seriously consider switching to it.
Hope this helps.