To make a Ghost baby, set one of your female Sim's traits to Kleptomaniac. Go to the graveyard, and have the Sim steal male remains. A ghost will appear 11:00 P.M. and disappear at 4:00 A.M. on the second day after stealing the remains. It will continue to appear every other day. Socialize with the ghost every time it appears and become best friends with it. Get the "Fertility" award and confess your attraction to the ghost. Ask the ghost to snuggle on the bed, and kiss him. Try for a baby every night and you will eventually have a ghost baby.