I think at least somebody made an exporter or converter from anim8or to b3D. Not sure if Anim8or is using bones internally. if it doesn't then it would make more sense to use 3ds.
Pacemaker is the recc. tool, It's not only very powerful, but also a product of an original blitz user. You may also use CharacterFX, it's not bad, but it seems further development is frozen. And then there's also Fragmotion. Finally there's a tool by Andrea, "Blitz Animator" or something like that, that is free and even open source.
See also toolbox:
http://www.blitzbasic.com/toolbox/toolbox.php?cat=6To answer your initial question: b3d to 3ds
If a b3d file is using boned animation then this cannot be converted to animated 3ds. The model may be converted as a static mesh.
The only tool that properly inmports B3D that I know of is UltimateUnwrap3D, or UU3D. It allows to im/export in many formats