FSSkyWorld was made AFAIK by one of the Active Sky Graphics people. It's like a freeware ASG for FS9. Great program! Shame no one's made something like that for FSX so people on tight budgets can get in on the awesome cloud action.
Lovely skies there, and I think I detect REpro in action for the water...
I must tell that the FS SKyWorld 2004 clouds (and I say ONLY THE CLOUDS, NOT THE SKY COLORS) will work with FSX retail. I think it worked with SP1 as well, but I'm not too sure anymore.
I WISH somebody would find a way to convert the SkyWorld textures in FSX SP2-copmpatible format. Even DXTBMP is not able to load those textures, I just see them in weird yellow/green/fushia colors :/