We are trying to achieve a similar thing, with a Vauxhall Vectra. Do you have any more information about the Vectra CANBUS? Or rather CAN Buses, because we learned that there are three.
We are at the point that we are developing our CANBUS scanner to find the can bus speed and communication parameters. Next step will be sniffing messages and some reverse engineering to get the info we want.
Did you manage to do some reverse engineering?
Our blog to track our progresses is http://hackingvectra.blogspot.com