From CNBC Like brick-and-mortar retailers, casinos in Las Vegas—and pretty soon in Atlantic City—are finding themselves up against a familiar foe: the Internet. It may seem counterintuitive that Nevada and New Jersey—homes to the two biggest gambling cities in the country—are leading the charge at the state level to legalize online betting. But states, like many Americans, are looking for new revenue streams as the economy continues to sputter to life. And some casinos are being proactive, looking for ways to develop or partner their way to a Web-based gaming presence. In February, Nevada become the first state to approve…