Back in the day when I was rockin' my strawberry iMac (at least it wasn't grape), I discovered Tiger Tech's Holiday Lights. It allows you to select from a variety of lights and other holiday-specific decorations (not just Christmas) that form an animated border around your display. Today, there's a very similar app for Mac OS X called MacLampsX that looks and behaves just like Holiday Lights. A customizable screensaver and holiday music is also included. MacLampsX is free. Check it out.