comTrace
ComTrace is a tool that will intercept both calls made on your interfaces and calls made to the COM library, and trace these for you. You will see the name of the method call, the parameters passed to the method and the returning HRESULT.
Interface definitions
In order to trace calls on any interface, ComTrace needs to know the signature of the interface. Interfaces that has a corresponding typelibrary will be traced automatic since ComTrace can load the typelibrary at runtime to learn the signature of the interface.
For interfaces that doesn't has a typelibrary (such as custom interfaces), ComTrace has a directory from where it parses IDL files to learn interface signatures. If your interfaces don't have a installed typelibrary, you can copy your IDL files into the \IDL directory (for instance C:\Program Files\ComTrace\IDL).
Screenshots
For a screenshot on ComTrace in action, click here!
For a screenshot on ComTrace hooking into a OPC Client, click here!
Download
comTrace runs on Windows 2000 and Windows XP (no support for Windows Vista). comTrace is free and you can get the setup here: ComTraceSetup.Exe.
Disclaimer
comTrace, AND ANY AND ALL ACCOMPANYING SOFTWARE, FILES, DATA AND MATERIALS, ARE DISTRIBUTED AND PROVIDED "AS IS" AND WITH NO WARRANTIES OF ANY KIND, WHETHER EXPRESS OR IMPLIED.