In the past, benchmarking I'd seen with Windows XP environment showed minimal improvement with striped disks using the onboard "Fake Raid" controllers over that provided by a single disk. (Contrasted to the Linux environment, where setting it up is a bit more complex but throughput improves much more as you'd expect).
I don't know if Windows 7 is any better - but regardless of OS version, striping disks doubles your risk of drive failure and eliminates the use of some pretty darn handy Non-Windows tools.
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