MTxAS object is replaced by COMSVCSLib object:

Dim objContext As COMSVCSLib.ObjectContext

In your VB project set reference to "COM+ Services Type Library" (COMSVCS.DLL) to use these objects.

I was learn from book "Active Server Pages 3.0 - Professional programming", published by Wrox press, so I cannot point you to some articles in Internet. But exploring this library in Object browser will show you that COM+ services are the same as services in MTS.