Depending on the model year of your car you may need the diagnostic wire (this comes with the CC kit anyway) however the likelihood is, it will be fitted from the factory. The other requirement is a compatible steering control module, it needs to be a midline or a highline, the later will also allow a MFSW to be fitted.
I have retro fitted CC in to swmbo's MY2007 Golf GT and my MY2006 vRS, I got one stalk from another member and the other from eBay, less than 40 quid each, took me less than 30 minutes to fit the first one, but only 15 the second time around. I then paid a visit to a local VCDS owner who for a small fee (4 x cans of the black stuff) completed the coding.
If you are not happy to try it yourself as it does involve removing the airbag and steering wheel, then Eddie-NL supplies and fits for silly money......
http://www.mk5golfgti.co.uk/forum/index.php?action=profile;u=2345