This is a scripted modifier. To use this script - place it in your scripts/startupscripts folder and restart Max. A new modifier will be available called Three_Fing_Hand. Add this modifier to your hand control object and wire your fingers to the sliders in the modifier. In the setup rollout of the modifier you can set your own high and low values for the sliders as well as save off presets for the sliders that can be used to make animating faster by being able to get back to commonly used hand positions.
This is only needed for Max4 users because the CA's don't work with the merge animation tool. Use a combination of CA with the PEN Attribute Holder script and you can do any interface that you like with more control and options.