Hi Pascal

For sales the procurement is created on the action_ship_create method, specifically this line build the values for the procurement and create it

vals = self._prepare_order_line_procurement(cr, uid, order, line, group_id=order.procurement_group_id.id, context=context)
ctx = context.copy()
ctx['procurement_autorun_defer'] = True
proc_id = procurement_obj.create(cr, uid, vals, context=ctx)

At /openerp/addons/sale/sale.py

For purchases the procurement is created on the make_po method, specifically this code build the values for the procurement and create it

po_vals = {
    'name': name,
    'origin': procurement.origin,
    'partner_id': partner.id,
    'location_id': procurement.location_id.id,
    'picking_type_id': procurement.rule_id.picking_type_id.id,
    'pricelist_id': partner.property_product_pricelist_purchase.id,
    'currency_id': partner.property_product_pricelist_purchase and partner.property_product_pricelist_purchase.currency_id.id or procurement.company_id.currency_id.id,
    'date_order': purchase_date.strftime(DEFAULT_SERVER_DATETIME_FORMAT),
    'company_id': procurement.company_id.id,
    'fiscal_position': po_obj.onchange_partner_id(cr, uid, None, partner.id, context=context)['value']['fiscal_position'],
    'payment_term_id': partner.property_supplier_payment_term.id or False,
    'dest_address_id': procurement.partner_dest_id.id,
}
po_id = self.create_procurement_purchase_order(cr, SUPERUSER_ID, procurement, po_vals, line_vals, context=context)