system updating with synaptic - shortcuts

[david]

Greetings,

In order to avoid a 400MB+ download I have /var/cache/apt on cd. So,
when I hose my install, I just reinstall and copy the cd to /var/cache.
However, I still have to add the sources to synaptic and click on the
Refresh button. What does synaptic download when I do this and where
does it keep them and can I add these files to the cd and copy them in
manually? The desired result would be synaptic updating the system
from /var/cache/apt without a net connection being present.
Is this possible?

many thanks

David