2) Don't tell anybody yet that this is going to be open source (yet)
3) Tell management that the days of paying up-front for software are gone. Vendors are now prepared to give you the software and the once you start getting "value" from it they will then kick in with appropriate user pays charges
4) Find a departmental or business unit sponsor who will give you someone to manage content. Someone who has their finger on the pulse in the business. ie the best office gossip!
5) Set up a post-nuke demo with all the modules you can find. ie weather, gallery, quizz, etc. Make sure you have some good themes to choose from and some ready made topics
6) Show the "gossip". They will love it, let them pick the sections, topics, themes and tune down the modules.
7) Gossip and sponsor agree to a prototype ( as there is no cost )
8) The support arrangements for the prototype are 4 months "best effort", at the end of that time the sponsor must go ahead with cost of full project. Make up a $ number here ( it doesn't matter ) but don't say "no cost".
9) After fabulous pilot of 4 months with no crashes and everybody loving the content you tell the sponsor that after all was considered an open source product did the best job
10) Put in place new an cheap maintenance agreement. Maybee even share the new user intranet $ charges with the sponser
11) Now you have a friend in high places - Go for the whole corp intranet....
Moral - Always remember how to eat an elephant - bit by bit...