You'll find the package names contain words quantal or raring. E.g. xserver-xorg-video-vesa-lts-raring
Those can be tricky to install because the process can leave you without X at all. Should that happen e.g. installing one of the Desktop Environments (gnome,kde,xfce,lxde) should fix it if you can't figure out a more subtle way of doing it.
