I use poser and lightwave quite a bit - more LW than P...

A much under rated tool for converting objects is Accutrans 3d. It's fully functional shareware, cheap to register, and and does a superb job of translating between formats. It can do quite a bit of cleaning up as it goes too, and the author is VERY helpful.

http://www.micromouse.ca/

For more heavy duty stuff with Poser in Lightwave, Greenbriar Tools is pretty powerful, (and also available for other 3d packages). I use it mainly for getting poser content into lightwave. It can get a bit more pricey with all the modules, but it does a good job. It's the best one I know for getting textures intact between programs.

http://www.greenbriarstudio.com/3D/

It's got some rather impressive options for getting models the other way too.

For using poser stuff in lightwave on the cheap I made a tutorial:

http://www.starbase1.co.uk/tutposer1.html

Part 2 still not written which will cover animating.

Nick