I tried this little printdir batch program too. Now all of my folders open with ACDSee, which is a graphics viewing program. The KB321379 article is clear enough, but unfortunately it doesn't work.
There is no "MODIFY" button in the EDIT menu where they say to change it. I thought maybe it was a permissions problem, but I have full permissions.
It also says, in HKEY_CLASSES_ROOT\Directory\shell, in the Value data box, type none. Well there is no Value data box.
So how am I going to get back to normal folder opening? This is a severe problem for me, as I'm constantly opening folders.