Adding fields to admin forms

[adarnaud]

Hi, I would like to add my own field to the form to edit users in the admin. It looks like this article
http://dev.osclass.org/2012/08/27/customize-columns-and-data-in-admins-tables/
 has a solution but the example plugin can no longer be downloaded (file not found). It it available somewhere else ?
Also I am using the LOPD plugin as an example of how to add custom field, and it uses hooks for which it seems there is no documentation : admin_items_table, items_processing_row : may be they are used in this missing example plugin ?

Thanks,
Arnaud