It may be too late for this reply, but I have to disagree with dean_palmer regarding the amount of priming sugar to add. Many sources recommend using about 1/3 the ratio of priming sugar for priming in the keg versus bottling. That is, if you use 4.5 oz of priming sugar to prime a 5 gal batch in bottles, use about 1.5 oz of priming sugar to prime a 5 gal batch in a 5 gal keg. I have keg primed several times, and my experience bears this out -- I usually use between 1.0 to 1.5 oz of priming sugar per 5 gal, and I find it to be just about right. Then again I prefer most beers a little on the low side of carbonation, so YMMV.
It's something to do with the ratio of headspace volume to total beer volume being different in a keg situation versus bottles.
Anyway, let us know how it works out!