If you have lost the "car pass" card (which has the immo, radio and key codes on it) you will have to get another from Vauxhall. Used to cost about £20.
You will also need to get the new fob coded to the car, which has to be done using a diagnostics system such asTech 2, vaux-com etc., not sure how much that will cost, depends on whether you can find an independent with the correct equipment or have to use the dealer.
vaux, November 2009