Not as far as I know. Since moving to Windows 7 is optional, and OneCare will run on up to 3 computers for a subscription, if you upgrade to Windows 7 and no longer use OneCare, that's your choice - and a good one, actually, in my opinion.
On Windows 7 you can run Microsoft SEcurity Essentials, which is the free replacement for OneCare -
http://www.microsoft.com/security_essentials/-steve
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