VBA does not have any direct access to all of AutoCAD’s curve analysis functionality (unlike AutoLisp, VB.NET, etc). There is a third party hook out there; search for Curve.cls and Vlax.cls. That hook, unfortunately, has a couple of problems that may crop up in certain situations.
It is possible, however, to mimic some of those functions mathematically. For instance, to subdivide a polyline bulge see the attached examples (DWG and XLS).