New York City Sublease Problem

My question involves landlord-tenant law in the State of: New York
I am the tenant of a 2 bedroom apt. in NYC and subleased a room out a few months ago for the remaining term of the lease (April 31, 2010). After only 2 months of occupying the room, the subleasee decided to move out with a friend. I was given 2 weeks notice before the roommate was going to move out. I told the person that I didn't mind the moving out part, as long as you can find a replacement to take over the sublease. This was agreed upon on both parties. A week later, the person approaches me and demanded I return the security deposit. I said that I would return it as soon as the new subleasee signs a sublease with me. The person didn't take it too well. The following week, I come home to find that the roommate moved all personal things and moved out taking the keys to the apt as well. I have filed a claim in small claims court for the remaining rent owed until the end of the sublease. I would like to know how strong my case would stand in court and what supporting laws support me as a tenant. Btw, I also have a letter from the landlord stating it was ok for me to sublease the room out so it is a legal sublease. Any help will be greatly appreciated. thank you

Presumably, you have a written agreement?

If you have a written agreement, you ought to prevail in court. If you don't, it's going to be tougher for you. Read here and here.