Perfect, thank you very much for your answers !! :-)

BR

Ricardo

you can achieve this using inheritance:

model.py

class groups(models.Model):
 _inherit = 'res.groups'
 # we inherited res.groups model which is Odoo/OpenERP built in model and created two fields in that model.
 field_1 = fields.Char(required=True,string="Field One")
 field_2 = fields.Boolean(default=False,string="Field Two")  

xml

<openerp>
    <data>
        <record model="ir.ui.view" id="res_group_form_view_inherited">
            <field name="name">res.group.form.view.inherited</field>
            <field name="model">res.groups</field>
            <field name="inherit_id" ref="base.view_groups_form" />
            <!-- <field name="groups_id" eval="[(6, 0, [ref('obe_core.obe_coordinator')])]"/> -->
            <field name="priority" eval="15"/>
            <field name="arch" type="xml">

                <xpath expr="//field[@name='name']" position="after">
                    <field  name="field_1"/>
                </xpath>                
                
                <xpath expr="//field[@name='user_name']" position="after">
                    <field  name="field_2"/>
                </xpath>        

            </field>                               
        </record>
    </data>
</openerp> 

Hi Ricardo Gross,
Actually, I did not get your requirement correctly,
If you want to add extra information in contacts (res.partner) you just do one thing,
Just inherits the form [ base.view_partner_form]

add the new field that you need in res.partner. and don't forget to add the fields in python files too.
Thank you.