Is it possible to open / edit a normal Visual Studio Solution with Visual Studio Express Edition ?
It depends. If this normal solution includes a unit testing project for example or a load tests or a modeling project (architecture, UML), then the answer is no. Class libraries, console applications, WinForm, ASP.NET, ... should be ok.
Yes this is possible with restrictions (not all project types are supported). You must edit the second line of sln-File. For example change "# Visual Studio 2010" to "# Visual C# Express 2010" This works for example for class libs or Windows Forms applications.