I've always bottled my beer after priming with sugar. Mix about 3/4 cup brewer's sugar in a small amount of water, bring to a boil for five minutes, then cool and add to my bottling bucket, siphon the beer on top, then bottle.
How does using wort to prime with differ from using sugar? That is, what are the differences in effect, and what amount do you use and what process should you follow? Also, do you brew a small batch of wort especially for priming, or just save some wort from your boil before you ferment? If making a special batch for priming, what OG do you shoot for?