Even if you think you can manage renting a car, parking alone would be a nightmare. Especially if you're not too familiar with the city and various traffic/parking laws. Depending on how long you plan to stay or if you can manage to stay with family for at least part of the trip...if you do your homework you can find a reasonable hotel in Manhattan, close to the subways where you would have access to just about any part of the city you wanted.

http://www.manhattanhotels.worldweb.com/