I've been wondering about that too. This thing keeps getting delayed. The latest news I found is from May 2009 and it says that they hope to sell it in 2011. Here's the story:
Zero Pollution Motors plans 2011 U.S. launch for 106mpg air-powered car - MotorAuthority
The web site for Zero Pollution Motors seems to be turned off. That's not a good sign. They were planning to make the car in New York.
The MDI web site still works and you can see it here:
MDI Enterprises S.A. - Air compressed cars - Flowair - Clean cars - Sustainable technology.