Both Windows 2000 and Windows XP are based on Windows NT and a short overview of Windows NT will introduce you to the developments built in to its successors. Windows NT is a multithreaded, multitasking operating system that runs its applications in protected-mode memory space. This reduces the risk of one application crashing the whole system. Windows NT requires a log-on, which then assigns security and control permissions through the user's profile. Windows NT is designed for use in a networked environment as a member of a workgroup or a domain.
Windows NT can run on a wide variety of hardware platforms, because it isolates any unique programming that is needed to support a specific piece of hardware in the HardwareAbstractionLayer (HAL). It also requires the hardware to be compatible and Microsoft provide a compatibility list for NT, 2000 and XP. You may find on occasions when you are upgrading machines that work well with Windows 98 that they fail to run NT and 2000. You will usually be presented with the blue 'screen of death' displaying a system crash. Fortunately, in an upgrade, this happens at the start of the upgrade not after you have spent hours installing everything.