The only thing I would add to what Slaven has said, is that if you are going to be doing development in Visual Studio with mojoPortal, use the source code not the compiled release. The source code has .sln files for Visual Studio. The release files are pre-compilled and have no C# source code included.
I use Visual Studio 2008 ,open the wwwroot foler with it.
Visual Studio supports 2 kinds of web projects, Web Sites and Web Applications. When you open a folder as a web site you are treating it as the web site kind of project, but with the source code, mojoportal is actually a web application type web project, which means all the code behind files get compiled into mojoPortal.Web.dll in the bin folder. Since you say "wwwroot folder" I know you are not using the mojoportal source code, but are using the pre-compiled release files.
To use the mojoportal visual studio solution you need VS 2008 SP1 with the Silverlight Tools for Visual Studio installed, as described in this article.
Best,
Joe