This Daily News article on Pre-Kindergarten registration had a graphic in its print edition that listed PS 101 as the 5th hardest pre-k in New York City to get into. You have a 9.2% chance of getting in. Admission is based on a lottery, not on merit. Children in the zone and siblings have first dibbs, but even they aren't guaranteed anything.
I don't know if every school has a pre-k program, but if you're planning on PS 101, you should have a back up plan. Like moving to New Jersey.