I have alwalys done this job with a wet process. Less dust. I use a compression sprayer to wet the ceiling first. I wet an area about 10x10 then I scrape it pulling a 6" taping knife over the surface. Don't push it, as if it is drywall, you'll damage the surface. The trick here is to get the texture wet enough to scrape, and getting the wet textrue off the ceiling before it thoroughly soaks the drywall. That's why I work with 10X10 foot sections. When I'm done scraping, I wash the remainder off with a sponge, skim over the seams and screwheads, and repaint.
This is a "skin the cat" job. I suspect that there are as many ways to do this as there are people who do it. I have found that scraping dry only gets the surface of the texture and leaves a rough surface that has to be skimmed over.
I'd expirement and see which process you like best. Remember, as Rick hinted, that this is a messy job no matter how you do it. Take the time to cover with plastic and dropcloths. Cover over windows and doors, remove all furniture from the room. Remember also that a plastic and dropcloth combination on a floor can be really slippery, especially when it's wet. I hope you have strong shoulder and arm muscles. If not, you have them when your finished!
When it's time to repaint, use a premium primer and finish paint. I recomend Benjamin Moore. "First Coat" primer is an excellent primer, and "Regal Wall Satin" is a fantastic finish paint for the do-it-your selfer. I always plug the "Mom and Pop" paint stores, as I feel you'll get better service from them than from "Big Box" stores. You'll pay a little more at Mom and Pop and you'll pay more for Benjamin Moore, but I assure you, you'll have less problems too.