Okay, I vaguely remember having to do this in VS2005 as well as VS2008 and have no idea why this is the default behaviour. It seems obvious to me that it’s useful to have multiple projects (read class library projects) with a web project under one solution in Visual Studio.

However, by default when you open a new project the project itself is the root of the solution and you can’t add another to it. Even if you create a blank solution file then ‘Add existing project’ it just automatically drills in and sets the first added project as the root and you can’t add any more.

Simple fix thought, all you need to do is:
Click Tools -> Options -> Projects and Solutions -> General -> check ‘Always Show Solution’

And you’re sorted.