I just cut my first keg today using a 4.5" grinder and cutting wheels. I don't consider myself particularly handy, but I do have a fairly steady hand. My step-father, who is quite handy said the one I cut looks better than the one that I bought off Craig's List pre-cut (apparently by plasma cutter).
The point of this is that it's easier to cut one of these than I ever would have imagined.
This site is invaluable: http://home.insightbb.com/~benschoep/keg/sankey.htm
Take note however, my step-father and I got 4.5" wheels because he had a 4.5" grinder which I smoked out during the cut. He was totally pissed (not at me at the manufacturer) b/c it was brand spanking new.
I went back to Harbor Frieght and got another of their Chicago house brand 4.5" grinders for something like $30. If I had done this project from the get go, I would have gotten the 4" grinder for $20, but since I already had cutting wheels . . .
I spent longer cutting and grinding to clean up the cut with the HF Chicago grinder and felt like the Kawasaki one I burnt out must have been an abberation.
Anyway, just do it. Use the outer rim as a guide and you'll make a perfect cut.
1) wear eye, hand and ear protection as well as long sleeves and pants.
2) after removing the sankey stem, fill the keg about half full of water to dampen the vibrations.