Karine123,
The Nook for PC program appears to still be available here:
http://www.barnesandnoble.com/u/nook-for-pc/379003591/
Nook for PC [download page]
I have this version installed on my netbook, and it is working / syncing up purchased titles. It worked fine a couple of weeks ago; it allowed me to download my approx. 20 B&N Classics Series titles. (Afterwards, I used the Apprentice Alf plugins with Calibre to remove the DRM. The "Alf'ing" was successful on all but one book).