The two locations in the Fort Greene and Clinton Hill areas of Brooklyn will start off with five cars each. Ten more cars will be added as the service ramps up and gains popularity. Residents of the Fort Greene area actually got a petition with 179 signatures of people interested in the services which they submitted to Zipcar to convince the company to set up shop in the neighborhoods. The available vehicles will include Mini Coopers, Priuses and pickup trucks.
[Source: Brooklyn Daily Eagle via Hugg, thanks to Linton for the tip]