An all-new PC form factor such as the tablet PC needs an all-new operating system, too -- an OS that can make new hardware features easy to use and quick to learn. Enter Windows XP Tablet PC Edition. This OS, which now comes preinstalled on all or most new tablets, is a modified version of Windows XP Professional, with a few extras. It includes new utilities -- namely, Journal, Sticky Notes and Ink -- that let you handwrite notes anywhere, as well as support for a variety of applications written specifically for tablets. Although Microsoft's new OS is perfectly suited for tablet PCs, we're not sure the tablet PC itself is perfectly suited to everyday use. If you're willing to take on a learning curve, though, Microsoft's new OS is the application that makes the tablet usable.