Microsoft (MSFT) late Monday announced that it will build its own tablet, called Microsoft Surface, to challenge Apple's (AAPL) dominant iPad. The Microsoft tablet line will run on the company's upcoming Windows 8 operating system, including Windows RT for low-power ARM (ARMH)-based processors. Microsoft's decision to enter the computer hardware business will put it in competition with its PC hardware partners, including Hewlett-Packard (HPQ),