This is the AS3 version.
You can get the AS2 version here
This file can be used without any actionscript knowledge.
The size of this file can be easily adapted to every width and height by simply setting of ContainerWidth and ContainerHeight parameters.
This Flash file can ben used as a source for NTSC and PAL Broadcast media as well.
Snow flakes size can be changed by editing MinFlakeDiameter and MaxFlakeDiameter parameters. Moreover you can easily edit: