1) 3DS Max 6, ZBrush
2) er, expensive I think. It was a \"present\" too
3) .3ds .max
4) .3ds .obj
5) 3, maybe?
6) Most people in my opinion use 3DS Max6, but it doesn\'t come with it\'s own built in .obj importer/exporter you have to download one.
Also I would go with .obj as being the main file format, I think everyone can export to that.