History of the iSight
Apple introduced the iSight at the 2003 Worldwide Developers Conference as an external unit that could be attached to a Mac.  In late 2006, Apple stopped selling these external iSight cameras.  iSight cameras have been built-into many Macs since late 2005.  Most new Macs including the MacBook, MacBook Pro, MacBook Air, and the iMac have a built-in iSight located at the top of the display.

Used by many applications
iSight is used by many applications on Mac OS X.  These applications include: iChat, Photo Booth, iMovie, and other third party software such as Yahoo Messenger for Mac.

Built-in iSight support for Windows via Boot Camp
Since version 1.1 of Boot Camp, Apple has included drivers for Windows installation running on a Mac.  Version 1.1 added drivers for Windows XP.  Version 1.2 added support for Windows Vista.