Cannot install vim

I really have no clue why the problem exists and how to solve it. I'm definitely not a sysadmin. I tried to use vim to edit the drush aliases file, when linux told me :

quickstart@qs10:~/.drush$ vim aliases.drushrc.php 
The program 'vim' can be found in the following packages:
 * vim
 * vim-gnome
 * vim-tiny
 * vim-gtk
 * vim-nox
Try: sudo apt-get install <selected package>
quickstart@qs10:~/.drush$ sudo apt-get install vim
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package vim is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'vim' has no installation candidate
quickstart@qs10:~/.drush$ vim
The program 'vim' can be found in the following packages:
 * vim
 * vim-gnome
 * vim-tiny
 * vim-gtk
 * vim-nox
Try: sudo apt-get install <selected package>

When I navigate to the Synaptic package manager UI, searching for "vim", I only find the package "vim-common" and 2 others, that are already installed, but no package for vim. It's strange because a few days ago I installed the latest debian squeeze in a VM with VirtualBox, and aptitude install vim worked perfectly.

Any hint ? I miss my Vim...