Does anyone have any thoughts on how to simulate a user load when custom ActiveX controls have been built into the page?

On our site we use ActiveX to provide client-side controls that allow the manipulation of a file (2D/3D rendering that the user can rotate, pan, zoom, mark-up, etc.) I've seen a suggestion to use VB to accomplish this...but I believe that would be single thread. One objective would be to test this functionality under varous load sizes.

Any thoughts would be appreciated.