(probably old news but I've not been trawling the 'net at my leisure for a while...)
MirrorMask is scheduled for worldwide theatrical release in 2004 :
Courtesy of Sci-Fi Wire
July 21, 2003
"Author-turned-screenwriter Neil Gaiman and visual artist-turned director Dave McKean revealed details and images from their upcoming feature-film collaboration MirrorMask in a panel at Comic Con International in San Diego..."
Gailman and McKean discuss MirrorMask at Comic Con (read full story here)