Well I'd say do it, and do it often. I have XP true, but I've been through all of the versions, and I still think it's a good thing to defrag it, it does help the overall funcion of your computer. Besides if you do it often enough it won't be such a hard workout ... plus if I remember right that silly msg doesn't mean a thing!
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"In the midst of winter, I finally learned that there was in me an invincible summer." ~ A.Camus