Yeah, thanks, this solutions works for me. i do that:

define in my class:

class stock_picking(osv.osv):
    _name = 'stock.picking' 
    _inherit = 'stock.picking'
    _columns = {
     'aux_almacen_orig': fields.selection(_buscar_shortname_alm,method="True", type="char", size=256, string="Almacen Origen" ),

then i define the function this way:

def _buscar_shortname_alm(self, cr, uid, context=None):
 obj = self.pool.get('stock.location')
        ids = obj.search(cr, uid, [])
        res = obj.read(cr, uid, ids, ['shortcut', 'id'], context)
        res = [(r['id'], r['shortcut']) for r in res if r['shortcut'] != False]
        return res

note: i define shorcut in my class stock location, this field only for to short the complete name in mi case, but you can change with another field that you have in your class:

class stock_location(osv.osv):
    _name = "stock.location"
    _inherit = "stock.location"
_columns = {
        'shortcut' :  fields.char('Nombre Corto',size=50),

and the XML file

<field name="aux_almacen_orig" />

and finally this is the result http://(w)(w)(w). orchidshouseperu.com/screenshots/Captura%20de%20pantalla%20de%202014-03-20%2015:52:20.png