apt-get install or upgrade from stored archive

[Antonio Rodriguez <arodriguez@worldnet.att.net>]

I had installed slink 2.1, which I upgraded through a my moden
connection after a few days to frozen. I made a backup of the
/var/cache/apt/archives folder in to another partition. After that I
messed up my system, so I had to reinstall 2.1 again. How can I apt-get
upgrade my system to the previous frozen status by using the backed
archive? The problem I see is that apt-get will have troubble
determining the dependencies, without a package.gz file, and there
wasn't any in the archive. Please help. I would hate to go through the
whole downloading thing again. If I fetch the packages.gz file existing
now in frozen, it will probably be different enough to be a problem.
Please give me some ideas for now and for future problems of the same
kind.
(Thanx)(10^6)
Antonio.