I think the Craftsman rototiller has a pin type hitch that fits on the back of every lawn tractor. Agri-Fab did make Craftsmans pull behind rototillers. Your 18hp MTD should have no problems. How big of an area do you want to till up for your back yard? Is there a lot of grass, (sod), still on top of the ground? If so, you'll have to make 3 or 4 passes over the grass to get down to the soil. How old is the tiller? Check to see how worn the tines are on the tiller. The more the tines are worn, the harder it will be to till your yard.
You might want to have someone with a garden tractor and moldboard plow turn the ground over for you first. Then you could use your tiller on it. If the tines are worn, the tiller wouldn't have as much trouble tilling up the plowed ground. I've been through this same process once before myself. That's why I keep asking to the condition of the tiller and the tines.
arthurb,