It's impossible to walk the streets of New York and not wonder what's behind the windows and doors of the city's panoply of residential buildings. Whether it's a breathtaking penthouse on Fifth Avenue or an inconspicuous garden apartment in the East Village, an artist's loft in SoHo or a private house tucked away on a quiet corner - New Yorkers know how to make their spaces both livablee and imaginative, both functional and spectacular.