WordPress MU

Hi there. :)
I already run a couple of single WP installations, and my job is webdesign and setup for clients.
I just started working for a firm with a couple of hundred members with the following requirements:

1. A single domain containing 1 website serving the firm and its members.
2. The firm needs to have a blog for themselves, and for now: another single blog where the members can post depending on their membership levels. Same theme across the blogs.
3. The firms static pages, their blog, and the memberblog needs to be available from a single menu on the firms page.
4. More memberblogs (maybe as many as 200) at the same site is likely later this year, using the same theme or optional themes. In this case the memberblogs will be listed another way, not in the main menu.
5. A single central admin environment with detailed control on each members/groups access to most functions.

Hosting is not an issue, just need to know if WPMU is the right way to go for this. Also I appologise if my English isn't quite up to spec, I'm Norwegian. ;)

Well, WPMU does most of things here.
Of course, you'll have to play around with plugins/tweaks/hacks.

Hiring a WPMU expert would be another good option for you :)

The challenging part when I started setting WP up for them was meeting the new requirement of multiple blogs in the WP setup, this requirement only came to light after working a few days with them. All the rest is ok and mostly set up allready through just the plugins/tweaks/hacks you mention. I'm guessing I'l just migrate to WPMU then and approach the task from that multi-user/multi-blog perspective, instead of their multi-user/single blog perspective. Considering the possibility of more blogs in the near future it might be foolish to build this up fully in just WP.

Basically, if you plan to manage more than 10 blogs - you should definitely go with WPMU.
Especially, if you plan to manage all the stuff yourself and your stuff is going to be quite dynamic - WPMU is your choice :)