[development] Altering the delete process of a node

Hi I want to alter the delete process of a node to add a new precondition. For example, I want to prevent the deletion of a document node if there are some categories (another content type not the Drupal category of the Taxonomy core module) associated with it. It's possible to add this precondition? Both content types are CCK related. Thanks in advance Ramon -- Ramon Vilar Gavaldà - http://ramonvilar.facil.cat - http://blog.facilitant.net Membre de FÀCIL - http://www.facil.cat Membre de l'esplai SESA - http://www.esplaisesa.org