Either the 22 or 25 will be fine (that is the width designation). I would personally opt for the 25's, they'll be a bit more comfy on rough roads.
As those are tubulars (as opposed to clinchers, what you are probably more familiar with), the tire will need to be glued to the rim. You'll need carbon specific glue. And it's sometimes helpful to put the tire on the rim before glueing to help it stretch out a bit making installation a bit easier. There are a multitude of tutorials on youtube on how to correctly install. Make sure to do it on a clean surface to as you'll be handling a sticky rim and a sticky tire and don't want dust or animal fur to compromise the surfaces. You'll also want to make sure not to get any glue on the rim sidewalls, or wipe it off properly before it dries (which could interfere with breaking).
Be sure you know what you are getting into, the care and maintenance of tubulars is quite different than clinchers, and changing a tire on the road can have it's own problems. For instance, you will need to carry a spare tire (as opposed to a couple patches), and would also probably want to take care on corners after replacing a flat tire (as the glue won't have had time to properly set and could roll of causing an accident). The gatorskins are tough tires though and once installed should mitigate many flats.
I personally enjoy installing tubulars, and have ridden quite a few sets. Before installing I would recommend at least watching some of the tutorials, back when I was a kid there was no such thing and my friends had a good laugh at my expense when I showed up in the park with my brand new wheels and tires... all covered in glue ;P'
Here's some interesting blog entries on the tire you mentioned:
http://www.thetallcyclist.com/2012/12/training-on-tubular-tyres/
http://www.thetallcyclist.com/2012/06/review-continental-sprinter-gatroskin-tubular-tyres/
