Regis,
There a few ways to do this and depending on the code some work better than others. You can register events for controls that are in a cluster the same way as any other control as long in the events you do not include the over all control as one of the objects event to be handled. so the object that you are looking for an event would be [mycluster.controlname, value change] or something like that.
The alternative and slightly more painful method is to just register the event for the cluster. Then using the refnum for the cluster and a property node take the controls array, which is an array of refnums for the all of the objects. Then you can poll the objects to see which one has had a value change. I have an example or two lying around if you are not following my explanation.
DAK