The previous one should still be in your /var/cache/apt/archives/
Not if you installed on a fresh machine last night! This is what caused my un-installable and un-removable gnome packages, which I struggled with for 3 hours and which meant that my users currently cannot log in under gnome.
--To UNSUBSCRIBE, email to debian-user-request@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmaster@lists.debian.org