Hello.
I've found this article about creating custom Movie Maker effects:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnwmt/html/moviemakersfx.asp
Unfortunately there isn't much information about the "Filter effects".
There are 48 different effects, but only 4 of them seems to be
included as standard with Movie Maker, and the rest are not very well
described. Does anyone know where I can find out about what the other
effects does, and which parameters to pass to them.