Apple iSight and most all other cameras you have working on Mac OS X are now shared with Windows virtual machines.
They should be available and work fine in Windows without any additional settings. Though if you prefer to keep your cameras separate between Mac OS and Windows virtual machine, please go to your virtual machine's configuration -> Hardware -> USB & Bluetooth (USB Devices in Parallels esktop 7) and remove a checkmark from webcams sharing:
in Parallels Desktop 11:
in Parallels Desktop 8 and later:
in Parallels Desktop 7: