Hydrogen is going to be big! Sure, sure, you've heard that one before, but this time, just maybe, it's for real. President Bush is touting it as our near-future Freedom Fuel, GM and Toyota are racing to bring the first production-model fuel-cell cars to market, and everyone and his hippie uncle is dreaming of a day when hydrogen-powered SUVs emit nothing but water vapor. There may even come a time when we're able to produce it by harnessing energy from the sun, wind or waves instead of from natural gas. Meanwhile, though, as we await that glorious future, it's easy enough to cook up some pure H2 on your own.