The "Worst Case Scenario" thread brought back a memory of a TV show that I thought you might all be interested in.
FOG was mentioning that it shouldn't be hard to retrofit cars to run on hydrogen. Turns out he's right, as long as the car is carburetted.
The show Mythbusters was testing methods of saving fuel. You've all seen the crappy infomercials, so they were testing if any of these products were actually worth money. To test, they had an early 90's Accord, representing fuel injected cars, and a late 70s Oldsmobile Omega, representing carburetted cars. They tried all the fuel saving methods on both cars, and they all failed, some even made the mileage worse. Then they tried this special method they found on the internet of making a carburetted car into a hydrogen car. First they disconnected the fuel line. Then they built a special box to go where the carburettor was, and pumped hydrogen from a tank into that (they were just trying to start the car, not drive it). The box was built wrong and didn't work. So, they gave a very stern "Don't try this at home kids", and stuck the hose from the hydrogen tank right into the hole where the carburettor was, and started the car! It ran for about 15 seconds, then they had a minor backfire which scared them and they stopped the experiment. My point, however, is that it obviously can't be that hard to make one of those cars run on hydrogen - just pump in the hydrogen and seal it up to prevent what happened to them.
Pretty cool little finding, I thought.