creating a multiple publication portal

Hi All

I am currently working on a project where we are creating a portal to various publications. Users who are registered with the site can subscribe to various publications.

Each publication has content which may vary greatly in content structure.
Each publication will function as a subdomain -> and will be to seperate publications with seperate look and feel.
There will be some generic portal functionality (glorified breadcrumb) to get back to the portal section aswell as some publication specific functionality.

My question:
What would be the best way of architecting a portal such as this in the context of Rails (2).
One way, would be to have a seperate app with shared sessions. Another way would be to extract publication specific code to a set of plugins or mixins.

Any quidance would be appreciated.