WordPress Site and Intranet on same host

Hi there

we currently have wordpress setup as a CMS for our actual website. I also want to setup wordpress to create an intranet for employees to have access to guidlines, documents, news etc. I want them on the same webserver so that
http://www.site.com goes to the website
http://www.site.com/intranet goes to the login for the intranet cms

what is the best way to set this up? do i add a subdirecty and put a new wordpress installation in there? do i setup multisite on the website wordpress and run it like that? I dont want any of the employees to have access to anything on the website.

Cheers