[rolgiati]

Simple recipe; you need abiword installed.

- Put all the .doc files in one dir or dir tree.

- Open a console, cd to that dir, or to the root of the dir tree.

Run the command:
find . -iname '*.doc' -print -exec abiword --to=html {} \;

Go to calibre, add the books from the dir or dir tree, select on
formats:"zip" and not formats:"XXXXX", convert from .zip to XXXXX.

PS Does not work very well on .docx from what I tried.