I guess you need
db.define_table("tblDriver",
Field("DriverName",'string',label='Driver Name'),
Field('id_tblVehicle', db.tblVehicle,label='Vehicle Name'))
db.tblDriver.id_tblVehicle.requires=IS_IN_DB(db, 'tblVehicle.id', '%(
VehicleName)s')-- Bruno Rocha [http://rochacbruno.com.br]
