Well, i finally managed to get this done yesterday!
It was a bit of a pig but not too bad in the end. My canbus was buried above the accelerator pedal. Once i removed the drivers side cubby hole i could just about see a red tab poking out but it was behind a load of other stuff and i couldn't reach my hand that far back. Until i realised that some of the stuff in front of it could be unclipped. Once that was moved to one side i could tease the old gateway out and simply unplug it and plug in the new one. Not too bad in the end.
Thanks for the pointers all!