If you only want 2 VIs to talk to each other, there is no reason to use ActiveX. There are several simpler (and probably faster) methods to do this (globals, functional globals, VI Server, Datasocket, TCP, DLLs to name the main ones). Some of these can also be used for programs not written with LV.
You can find more about communication in the LabVIEW user manual. You can find several examples in the LV example finder. Also, try searching this site and google for LabVIEW and ActiveX tutorials.
Here is a LV tutorial. You can also contact your local NI office and join one of their courses.
In addition, I suggest you read
the LabVIEW style guide. If I remember correctly, it may discuss this as well.
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