you can make any 2.3 file set snow but you need to build it into the map if that makes sense.... i did it for last years christmas event
if you guys know how to play around with the map builder you should be able to recreate the effect but here is the files i used
http://www.mmorpggeek.com/christmaspatch1.rar
it should have 1 snowy map and falling snow (the falling snow isn't amazing as its a bit of a repetitive loop but it impressed the players on my server enough to make them think the event was great lol

)
the map itself is just a large open snowey area so you can do pretty much what you like with it
hope it helps someone out (and is the first map i made and have released lol)
(im sure Lifco's snow will be far superior though so dont assume this will be as good as his :P)