Hewlett-Packard (HPQ), which has rewarded investors with a dependable stream of earnings growth for years, is on a buying binge, retooling itself to keep in touch with tomorrow's business. Last month, the Palo Alto, Calif.-based computer giant agreed to buy 3Com (COMS) for $2.7 billion. The deal, assuming it goes through, will help fortify its position in the corporate data center market. The industry is becoming dominated by a few big players who