Is it simply as easy as buying a sony stalk and that will work on teh MK2 and the Vectra steering wheel controls ?
The Sony Stalk is a third-party joystick that attaches to the side of your steering column. If you use a Sony Stalk, it will not work with the Vectra steering wheel controls, it will bypass them completely and you will use only the Sony Stalk.
If you can find a stereo shop which happens to have a Vectra-To-Sony adapter system (I do not know if such a system exists or not), then you can plug that into your Vectra, and plug the other end into the Mk2 tuner module, and it should work.