ohn Hancock Mutual Life Insurance Co. has a new intranet-based corporate purchasing system. The company spent $337 million in 1997 on supplies needed to run the business, but only $28 million - 8% - went through the central purchasing department. With its new intranet system in place, Hancock expects to boost that figure to 85% without any increase in staffing. Not only will that let Hancock reduce paperwork, increase accuracy, and speed the processing of orders, but it also will maximize leverage with its suppliers by centralizing bids and guaranteeing the purchase volume of just about anything it buys. Although the potential benefits of such a system are enticing, the software is expensive, and the installation is complex and labor-intensive.