Sometimes classes are seperated i different assemblies and you need to load classes from a specific assembly. Here is a way to load a class and instanciate a variable of that type:

try {
System.Runtime.Remoting.ObjectHandle objHandle =
    System.Activator.CreateInstanceFrom(Application.StartupPath + @"\MyAssembly.exe", @"MyNameSpace." + @"MyClassName");
} catch(TypeLoadException) {
    // Problems loading class
}

if(objHandle != null) {
    MyClassName myObject = ((MyClassName) (objHandle.Unwrap()));
}

If you want to create an object instance of an object in the current assembly, simply use: System.Activator.CreateInstance() with the number of arguments needed for the types constructor.