Following the passage of a bill last year that prohibits online gambling, Linden Labs has invited the FBI into Second Life to figure out the propriety of virtual casinos that have popped up there. LL is unclear whether wagering in a virtual casino with virtual money, which can be converted to real money, is illegal under the new legislation.
FBI Investigates 2nd Life Casinos
I do not see why this would be any different than other online gambling. Usually the whole virtual currency things throws bureaucrats for a loop, but people gamble with virtual money all of the time: they're called chips.