Loading OBJ files is not really a problem but I have troubles in making anything "conforming" or "fitting" Every time I import and OBJ it seems to have a "random" size. Even if I import different parts of the same mesh I have to scale everything again. What is the thing I am doing wrong ? I use MAX with the habware OBJ exporter plugin.

Could be several things but if it seems to be random for different parts make sure that not any checkboxes in the import dialog are checked. It was quite a time ago since I last did it but I think you can remove them all, at least make sure you dont check any scaling and center boxes.

Ditto. If you've already scaled the things to match, uncheck everything on the OBJ import panel. You're probably getting random sizes because the "percent of figure size" is checked. This tries to adjust every OBJ to the same size.