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Don't even consider upgrading a desktop or laptop to Windows 8 till Microsoft releases Windows 8.1. The interface of Windows 8 is biased towards the touch screen interface, and Microsoft removed the "Start Button" which will be added back to Windows 8.1.
Also, Windows 8 eliminates support for Open GL in video cards when using Windows 8 certified drivers. This means a major decrease in performance of many video cards after "upgrading" to Windows 8. If you're not going to buy a new computer with Windows 8.1 alreading installed, you're better off upgrading to Windows 7 which will be supported till January 14, 2020.
Your Windows XP workstations are all running the 32-bit version of Windows (almost everyone is), which means that they can only run 32-bit applications. The 64-bit version of Windows 7 is by far the most popular, and Server 2008 R2 only comes in a 64-bit version. It's highly-likely that Windows 8 will also be 64-bit only, and that will mean that when you make the jump to the new operating system, all your apps should be 64-bit capable. You may want to wait until next year when Windows 8 is out, rather than worrying about the migration now. After all, how many times was Windows Vista delayed? I would never hold my breath based on a Microsoft calendar.