Just off the back of a thread in GD about using a webcam as a security cam, there is a piece of software called EvoCam which allows you to use your iSight as a security camera. Ive got it and had a play with it on my Intel iMac and I must say its pretty good. It allows you to set up things like motion detection areas within the sight of the camera and upload any pictures or movies taken to a remote server, an email account or a local folder.
http://www.evological.com/evocam.html
http://www.evological.com/evocam.html