For those who own facelift Omega's this may be of some help.
I bough and fitted a used cruise control stalk to my 2000 X reg 2.2CD Omega saloon.
I took it to a vauxhall main dealer service centre in Yardley Birmingham (there's only one so it's easy to find out who they are) and it cost me £53.46p to have cruise control enabled. This may not be the cheapest but they only had the car for a coupe of hours and I now have a very smooth cruise control facility on my lovely 'Meega.

To reitterate the existing information on this site, Facelift Omega's only need the stalk fitting and cruise enabled with Tech 2 equipment. Nothing else is needed because the electrics are already fitted to the car as standard. The stalk I fitted to my car had the additional small 4 pin plug loom attached. It was a little awkward to find the small socket to plug the stalk loom into 'cause it was tucked in behind the stalk site main body and need to be fished out a little. It took about 10 minutes to fit the stalk and the only tool needed was a medium length cross head screwdriver for the 5 screws (three underneath the steering cowling and one to either side of the steering wheel with a plastic cap concealing them. Accessed by turning the steering. It's also handy to unscrew the steering adjustment lever and remove the two halves of the plastic cowling. I checked that all normal functions (indicators etc) were working before putting the cowling back on. Sorted.
Total cost to get cruise up and running was £75. Well worth it me thinks........
Worm