> when i download a site with microsoft documents, it stores
> theme in text format (i suppose), because when i click on
> the download link, i got the textual content of the file.
> On the original site, the server seems to send the correct
> mime type because words or excell opens up.

The fact that IE does successfully open a document does NOT 
means that the remote server sent the correct mime type, as 
IE is doing horrible hacks to detect the document type by 
looking at its contents.

First try to erase all demaults MIME types (Options/MIME 
types) and rescan the files.

The wrong mime type may also be sent during the HEAD 
request used to detect the type, in this case use 'Use old 
http/1.0 requests' option.

> ps: êtes-vous français ? 

Absolutely :)