Not only home users are customizing their computers into the holiday winter spirit, but webmasters also. Here is a scrpt that will add a snowstorm to your HTML/PHP pages without being hard on the eye or intrusive. The JS can also be customized by setting the ammount of snow, the wind and if it should collect or rapidly melt. The only drawback to this script as most JS is that some users may find your page loads rather high.
Download the SnowStorm JS, which also includes a demo page and source code.