For strongly-named NET assemblies that are registered in the GAC, you can just use the assembly name
e.g: $x = new DOTNET ("myAssembly", "myClass");
For strongly-named NET assemblies that aren't registered in the GAC, you need to use the full assembly string
e.g. $x = new DOTNET('myAssembly, Version=X.X.X.X, Culture=neutral, PublicKeyToken=ZZZZZZZZZZZZ', 'myClass');
You can't instantiate assemblies that haven't been strongly named.
"Strongly named" means that the assembly has a public key. To strongly name your own classes in Visual Studio, go to the Signing tab in the project properties and click the 'sign the assembly' box and choose a key file name.
To register an assembly in the GAC, there are various tools around to do that, but the easiest method is to drag-and-drop the compiled assembly into c:\windows\assembly using windows explorer (a shell extension is installed by default that handles registering dragged files).