By Paul Carsten BEIJING (Reuters) – A Chinese regulator said on Tuesday it is conducting an anti-monopoly investigation into Microsoft Corp over its Windows operating system, in the latest in a growing number of competition probes that have unnerved Western firms in China. China’s State Administration for Industry & Commerce (SAIC) was also investigating a Microsoft vice president and senior managers, and had made copies of the firm’s financial statements and contracts, the agency said on its website. It said Microsoft, which has struggled to make inroads in China due to rampant piracy, had not fully disclosed information about Windows and its Office software suite. Microsoft is one of the biggest U.S.