Architecture for humanity is helping get volunteers for the 2010 New York Homeless Survey. They still need volunteers in the Bronx and Staten Island.
Here are the results of previous surveys. most of the homeless live in Manhattan and on the subways.
For those really interested in understanding homelessness: Here is an anthropology paper with a little story about drug dealers and homeless people mixing with anthropologists. It shows that in these groups respect is earned and not given automatically. Accessing Distrustful Populations: Lessons from ethnographic research with the street homeless
For a specific study or female homelessness this book may provide insight.Silent Sisters: An Ethnography Of Homeless Women