A Ventura County investment broker was sentenced to six months in federal prison for his role in an alleged money-laundering scheme that prosecutors contend was directed by San Diego financier Richard T. Silberman. Terry Ziegler, 45, of Moorpark was ordered to surrender July 26. He had pleaded guilty two months ago to a single felony count. Originally accused of executing the complex financial transactions involved in the case against Silberman, Ziegler pleaded guilty to violating a federal currency law. Meanwhile, a federal court jury will begin deliberating Silberman's fate today. Silberman, 61, who once was a top aide to former Gov. Edmund G. Brown Jr., is awaiting the jury's verdict on seven felony counts involving the laundering of $300,000 that authorities said were Colombian cocaine profits.