From asp.net/mvc i downloaded the MVC 3 Installer, and ran it:

When it finished, i loaded Visual Studio and tried to create a “New” Web-site. But there’s no option to create an ASP.NET MVC web-site:

i expected to see something like what’s shown on the ASP.NET MVC homepage:

There is also a Getting Started tutorial that lists the steps to follow:
Creating Your First Application
You can create applications using either Visual Basic or Visual C# as
the programming language. Select Visual C# on the left and then select
ASP.NET MVC 3 Web Application.
After that didn’t work, i also tried:
a web platform installer
another Web Platform Installer (from the MVC3 homepage)- or download the installer here (also from the MVC3 homepage)

Click on File -> New PROJECT (NOT WEBSITE). it should be in your list