you dont decompile msz files (or shouldnt) thats what the majority of modellers use to show previews of thier models before they are released to view in 3d on a webpage, ie. the milkshape viewer
there are no decompilers for msz files, (public ones anyways), prettymuch all it would be good for is decompiling peoples models that made a preview of it and didnt want to be released yet, its not really a file made for importing and exporting, its just the package file that the ms3d viewer reads from, not meant to be editable