I don't know about .3ds either. But I can import a .dxf that's about 2.89 MB. Bryce freezes if it's much over that. Sometimes it surprises me, though, and will bring in a larger file. (That's usually when I've left the room and ignored what I thought was a frozen app. You know, the "watched monitor" syndrome.) I immediately export it as a .3ds to bring the file size down.