I suppose that sometime I'll turn this into an actual article or something, but in the meanwhile here is a bit of a note that I wrote to a friend who wanted to know about hackling:
Hackling is drawing the fiber through a bed of nails or a toothy thing, whereas combing you use a set of combs, and lash the fiber on to one and use the other to comb it off, or use a comb to comb a lock like hair. Although some of the ones you see are sharp, they don't have to be sharp to work. One of my favorites is just a little metal florists frog screwed onto a handle, another is a big dog comb, bought in a pet store. You can also use one hand card, hold it onto your thigh, and draw a lock through the tines, reverse the lock, and draw it through again. If both hands are free, you can use one to press the fiber in and the other to draw.
Here are some hackles [like I said, they don't have to be sharp, but some are. I would be sanding down those points.]:
and here is a showing a hackle used to blend: