Custom dispatch ID

Scenario:
I am trying my move my graphics engine to an MFC ActiveX project in VisualC++ 2005.

Primary question:
What range of dispatch ID's are safe to define in my own code? I will be using about 300 methods.

Secondary question:
Is there a good way to handle vectors (4 x float) and matrices (16 x float) in the ActiveX interface?

I can't answer your questions, but I can tell you that ActiveX in MFC is clunky at best.

Instead take a look at doing your ActiveX control with ATL. You'll end up with a lightweight control w/no MFC dependencies.