Virtual host using Instant Rails 1.7

I have developed an application called demo using Instant Rails 1.7.
How do I host this application say in development mode (as a virtual
host)? I already ran the two examples cookbook and typo packaged in the
zip file that are virtual hosts running on Mongrel and served by apache.

I just want to add my application (demo) as the third virtual host.

Really appreciate any help.