Question: I am creating an application where the user picks a value from a combo box, the application then selects that feature and then selects the corresponding features from a second layer, (both selections are in a different colour). What I want to do is as soon as the selection is made, the map will zoom to the envelope of the selected features. I know how to zoom to 2 individual layers (using pEnvlope.union...), but i need to do it on features.

Has anyone got any idea of the best way to do this?
(I'm using ArcGIS 9.3.1 and VBA).

Thanks

Answer: 
If you are outside of arcmap you would get the features geometries and use the IToplogicalOperator's union and zoom to the extent of the unioned geometry.
If you have info about the object, you know it's min/max X and Y's, so it's a matter of building some logic in the code tozoom to that envelope, taking into account scaling etc