Follow these:
http://www.blender.org/education-help/tutorials/
If you installed the correct python script you will be able to export to .3ds. However blender is an all in one environment and isn't really built for exporting all sorts of stuff. You will not succeed getting an object into NL if you try to animate, use UV Mapping or have any entity that is not a mesh i.e. scripts, lighting, pure particles and even the camera. Remove everything like that before even trying.
My proof:
[youtube]
http://www.youtube.com/watch?v=y5Th-p2Q ... r_embedded[/youtube]