Earthworms require several inches of organic sandy loam which will hold
moisture. If you don't already have these conditions, then dig an area in
part of your lawn (yard), make the necessary soil preparations and add the
worms. Earthworms also do well in soil that has coffee grounds sprinkled
over it. Their castings help to fertilize the soil around the grass roots.
Try these websites for help.

http://aggie-horticulture.tamu.edu/p...worm/worm.html

http://www.ars.usda.gov/is/kids/soil...2/goodworm.htm