IT ALL STARTED with a can of Safeway-brand beef ravioli. Jim Meehan, a San Francisco network engineer, had been reading on Slashdot (www.slashdot.org), the geek news site of record, about how to build a homemade antenna for his computer. The heart of the contraption was an ordinary metal can. "They recommended using Malley's beef stew for the can, but the ravioli was cheaper," Meehan confesses. After some tinkering and tests, Meehan discovered his home-brewed antenna was far from ordinary: indeed, it's possible Meehan's humble ravioli can, combined with the know-how of a few hundred community-minded geeks, could dramatically reduce the cost of high-speed Internet access for everyone in San Francisco. In some cases, access might even become free.