Access WebMatrix Project From Another Machine
By default WebMatrix projects, which run in IIS Express, are accessible only from the local machine using the localhost name in the URL. There are some situations though in which you might want to run the project on either the server name or an IP address so that someone on another machine can access the application for review.
The following page was written during the WebMatrix beta, but ignore the word "beta" because it works just the same now that WebMatrix is full released.
http://blogs.iis.net/vaidyg/archive/2010/07/29/serving-external-traffic-with-webmatrix-beta.aspx