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I don't know about an external one. My onboard iSight works just fine with Boot Camp 1.1 drivers. (Yes they're old.)
 
I tried to open the camera in XP and the system crashed. The camera shows up as a device with it's own icon so I thought I would give it a try. Unless it has changed with the latest bootcamp update then don't try it.
 
Works for me, but I didn't do anything with it other than check the image. Built in on iMac 24".
 
The OP is talking about an external iSight and not the built-in ones found on the MacBook/Pro and iMac.

Just for clarification.
 
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