Two question: Have you ever been bitten by the Windows 2000 RPC bug? Have you thought of an OS tweaked or designed for real-time processing, like RTLinux or VXWorks?
On my laptop I am still running Windows2000 due to XP not playing well with a proprietary communication driver. XP runs on my desktop for AutoCAD, most office stuff. As far as the process simulation goes, that's the Mac. So the marketing of the Mac is towards graphics and art types, and libs. I have been using the Mac in its various forms for realtime modeling (mostly for control systems validation) since the early nineties. And the drivers are there for Allen Bradley, Modicon, Honeywell, Foxboro, you name it. Of course now OS-X is UNIX.
And I do have one platform that runs '95, and will never be upgraded. The big reason is its ability to run old DOS programs, which are used for programming some early (as in 1980's)PLC's. Big market for replacing these old control processors, yet I still have to be able to extract and print out the old program to configure a more up to date replacement (think replacing an old Westinghouse NumaLogics with a much more current Allen Bradley).