there is a guy on here "metroMPG" that is getting unbelieveable mileage. he has also done some radical modifications to his car to get there. I think the wildest was a transmission swap but he got really good gains from doing it. this may be the secret to getting the gas mileage that you are talking about.
my first car was a '93 geo metro with 3cyl 5spd and power nothing (maybe breaks) I dogged the crap out of that car. when I got rid of it in '99 I was still getting 46mpg.
that guy metroMPG has a web site
www.metroMPG.com he also talks about a car that got 75 or so mpg he has a pic or a link to a pic where the guy actually cut a metro in half long ways and reduced the drag on the car. it is weird looking but it got great mileage.
being a long time metro fan, I thought it was kind of cool. I had two, a '93 and a '97 they were both good on gas and both hatchbacks.