Hi Claudio,
Project-manager in HEAD uses dynamic-types to process aditional form elements.
Maybe you could see how dynamic-types works looking project-manager code. Install package and add new elements to pm_project object type or just take a look at:
http://cvs.openacs.org/cvs/*checkout*/openacs-4/packages/project-manager/templates/project-ae.tcl?rev=1.6
using dtype::form::add_elements and dtype::form::process
Hope it helps
