[Hampshire] Installed packages list - Debian

Dear List,

I have a small hardware problem with a debian system, the disk is
dead, but I have a tar-file backup of the filesystems which I can
restore. I want to extract from this the list of packages that were
installed, something like dpkg -l, if the system was running.

Does anyone know how I can point dpkg at the restored files ? or
another way of doing this ?

Alex,