pointing multiple domains to same instance of CI

[eluser]niyogi[/eluser]
we need to point multiple domains to the same instance of codeigniter. As the user browses from page to page, they should remain on the same domain. Does anything special need to be done to achieve this?

To make things a little bit more complicated we need each domain to point to a specific controller. How would we do this?

You're help is greatly appreciated!