Do I need to reinstall the whole system?

[Philippe Grenard <philippe.grenard@m4x.org>]

Hi all!

well, last time I did a dist-upgrade , the system hanged, and even the "magic 
keys" didn't answered, so I had to reboot the system.

After that, there was one package that i couldn't upgrade, nor install, nor 
uninstall. (xserver-xorg to be precise)

So after somme googling, I tried to edit 
/var/lib/dpkg/status
/var/lib/aptitude/pkgstates
and remove the entries of xserver-xorg
I also removed /var/lib/dpkg/info/xserver-xorg.* (preinst, postinst, prerm, 
postrm, and so on)

but the system still won't install the package. It always failed during the 
preinst script it seems :

 root # dpkg -i /var/cache/apt/archives/xserver-xorg_6.8.2.dfsg.1-9_i386.deb
(Lecture de la base de données... 134036 fichiers et répertoires déjà 
installés.)
Dépaquetage de xserver-xorg (à partir 
de .../xserver-xorg_6.8.2.dfsg.1-9_i386.deb) ...
dpkg : erreur de traitement 
de /var/cache/apt/archives/xserver-xorg_6.8.2.dfsg.1-9_i386.deb (--install) :
 le sous-processus pre-installation script a retourné une erreur de sortie 
d'état 1
Des erreurs ont été rencontrées pendant l'exécution :
 /var/cache/apt/archives/xserver-xorg_6.8.2.dfsg.1-9_i386.deb

( it's in french, but basically, it says that there was an error during dpkg 
during preinst script with an error or exit code 1)

Well, the questions are : 
- How to make the system believe that the package isn't (or is) install, in 
order to remove and reinstall it properly
- Is there a way to "run the dpkg process" step by step by hand with only some 
basic commands as cp, rm, mv, mkdir, .... to see where there is a problem
- any other idea?
- Do I need to reinstall the whole system?

I thank you all for any help!
I already tried a lot of google but i couldn't find a solution to this 
problem.
I also don't mind to read a lot of useful stuff if anybody has some ideas.

Thanks a lot for any useful link or idea!!!