iSight Screensavers is now free, so is no longer available for purchase. If you have Mac OS X 10.6 (Snow Leopard) or greater, you can install the latest version for free to get rid of the registration text. Download it here.

If you are using an older version of Mac OS X, then that update may not work. Here is a serial number to enter instead:
1VQ7-37LQ-2D2B-8SPJ-D1B9