Hm..as you said you have tried it with some older versions where you had to install the pandemic tool. What were if you use the latest xsi version and try the Zetools to im and export your models?
i don't think so. Most SWBF2 Models have only one model chunk, one shadow chunk, (optional) one cloth chunk and the skleton chunks, So i don't think you can take only the helmet by hexing it. Therefore you need to edit the model in XSI (open the stormtrooper, delete the helmet, place the new helmet, envelope only the new helmet to the head/neck bone
Look in the xsi faqs. There should be a link to zetools.
Zerools can export to msh and xsi can import obj, so yes it will help you to export onj to msh.
A while back, I hexed that yoke and hood onto Luke. No XSI.
Separating it out and consolidating it was a big hassle. (It would be easier and cleaner to use XSI.)
Someone used a different version for a mod, but here is that model: http://dl.dropboxusercontent.com/u/5836 ... d_Luke.rar
It has a version with both hood and yoke, and one with yoke only. They are their own, isolated chunks, so it should be easy to separate them in XSI or via traditional hex-editing.