ASP CMS Platform

I am looking for an ASP Open-Source/GPL/Paid Licence based CMS platform for our Intranet. We need the basic modules on there, such as;

User accounts with different access permissions,
News,
Updates,
Intranet Search,
Calendars (multiple ones if possible),
Basic output pages for documentation/Manuals.

Also if possible we are looking for the use of databases where we can add records of products easily for the Intranet user’s reference.

What is more important is the ability to easily intergrate/add-on mods/Applications with the software. Either we will write these ourselves (in time) or amend Open Source applications for our needs.

A site we have been looking at is Convea (www.convea.com). It is really similar to what were looking for to give you an idea - the problem is, is the user interface, lack of company branding etc, and not web-based.

An easy install would be great as we are fairly new to this We are running on IIS5 and MsSQL (with MySQL also for testing purposes). At the moment ASP may be better, but we will also install PHP.