Ok, been working on this off and on for a while. This post contains a download link illustrating how to implement a many to many relationship and then also demonstrates two alternative methods for making the necessary links between the two tables.
In addition to using a portal to the join table, there is also a layout where a diminishing value list is implemented as a way to keep the user from linking the same pair of records more than once. A third layout sets up a portal as a check box controlled list as yet another way to make linking selections between the two tables.
Each layout is copiously annotated. Notes have been included in the relationship graph--which is set up in Anchor Bouy format. Comments have even been added to some field definitions to help folks figure out how each part of the system works.