If you have a pre-facelift Omega (with a throttle cable, not DBW) then check out this helpful forum 'how-to' guide:
http://www.omegaowners.com/forum/YaBB.pl?num=1166374649Kits with all (or nearly all) the parts are going for between £30 to 50 on eBay.....or you could ask on the forum 'bits wanted' for the parts needed.
You need the cruise stalk, throttle-actuator, 4 terminal switch for brake pedal and if a manual-box a clutch switch too....that`s about it, all the wiring is already there, so it`s really a plug and play job: a good afternoon`s work or perhaps a day if you drink lots of tea/coffee and chat to mates.
If you have a Facelift Omega model; it`s even easier to fit....just buy the special (Facelift) cruise stalk and then have the car down to a forum member who can Tech-II enable cruise (or a dealer could do it if you don`t mind being 'taken').....there`s a Facelift Cruise 'how-to' for that in the maintenance guide too!
I`ve found it an easy-peasy job to fit.....