As Dan asked, we really need to know if you are trying to assign unique id's based on groups. Say if you have 2 polygons in a fishnet and each have a group of points inside each polygon. Would you want the IDs to be something like this:
fishnet polygon 1 point id increment: AA01, AA02... etc.
fishnet polygon 2 point id increment: AB01, AB02...etc
Or are you just looking to assign a unique id for every individual point?