I've decided that I'll release separate tools for extracting stuff from the gamedata instead of building a big extractor and work on it forever before releasing a stable version of it. This way people will be able to extract the things they want (e.g. music) without having to wait a huge amount of time only because something is not working properly with, for example, subtitles overriding.
Then when the big part is done, the tools will be merged within a single application (it will be a matter of merging ui's more than other).
At the moment, I'm learning Qt (4.3.0) for the GUI. When I'll be ready for a first release, I will open a sourceforge project page with all the sources and complete documentation. Currently I'm working under Linux so I guess I'll need some time for debugging under WinXP (where I already spotted troubles with read(2)).
I will update the progress here for those of you who are interested in this.