Twenty months ago, a pair of twentysomething buddies founded a company above a California pizzeria that let people post their favourite video clips, ranging from stupid pet tricks to rotund Plasticine hippos that sing.It was a wildly improbable business model, laced with the threat of copyright infringement lawsuits and stiff competition. But it worked.YouTube Inc. agreed Monday to be swallowed by Google Inc. for $1.65-billion (U.S.), a deal that may mark one of the fastest Internet growth stories since the tech heyday of the 1990s. More