You can have a portal like this one relatively easily. It is based on DotNetNuke, an Open Source ASP.Net portal platform that is highly customizable from both a developer and a user perspective.

DotNetNuke can also host multiple portals on the same site. Think about the possibilities for department or customer-level customized websites! Because the design of DotNetNuke is open, we can add complete containers of functionality, including eCommerce, Back-Office database applications, and Customer Relationship Management. There is even a basic eCommerce module ready to implement, and a community of module and skin developers. Please tell us what you like and don't like.