This code add an instance of a 'SpamProtecterField' class specified in SETTING UP THE MODULE section. The newly created field will have MollomField field. The first parameter is a Form object in which the field will be added into and the second parameter tells SpamProtecterManager to place the new field before a field named 'Message'. The last parameter is an object that get notified when the spam verification is done and given the form object.
The purpose of having callback object is we can process the submission differently according to the spam status of the submission. For example, put any submission with 'spam' status into spam queue.