What version of ACT are you using? In 2008, look at the Help file, "Scanning for duplicate records"; it lays it all out. You can set the duplicate parameters, then ACT will put up a list of all of the matching duplicates. You then should manually look at each pair (via a Copy/move contact data wizard) to see what may be different between the two alleged dupes. You can move data from one record to the other in the pair of dupes, then eliminate the unwanted member. It's pretty automatic, except for the need to scan alleged dupes -- but I am surprised by how many times I find something different between what I thought were members of an exactly duplicate pair.