You should google the address and see what comes up. If it is listed you should see the active listing and agent when you do that. If it is not for sale there will be only one result which will basically be the google map of the house. You can also go on web sites like www.PropertyShark.com or www.NYC.gov (do a search for BIS and/or ACRIS) to research more information on the property and it's owner.
If you want to purchase that property or any other for that matter, you should first get yourself pre-qualified by a mortgage banker to make sure you can get the loan and afford to buy the place! Unless you are buying all cash, then all you would need is a lawyer to help you through the legal process of purchasing.
Another option would be to have a licensed real estate agent or broker help you out. If you like I would be more than happy to help you with that. If you have further questions and/or concerns, feel free to contact me. Good luck!
Mitchell S. Feldman
Associate Broker/ Director of Sales
Madison Estates & Properties, Inc.
Office: (718) 645-1665/ Cell: (917) 805-0783