I need to build a COM DLL to do some simple serial port stuff.
It has to be a Class DLL (COM); I have no control over that. I also have no control over the fact that it has to run on some very old machines which do not have the .NET framework installed and never will have.
Can it be (easilly) done using VB Express 2008?
You can’t do it with VB.NET. There is no support for building .NET-less dlls in VS anymore except using C++.
VB6 is the last VB version to support what you want to do.