Trying to understand how checksums and signatures work

[Gilles Pelletier <gpel@vif.com>]

I found out the MD5SUMs are in the package itself but where are the 
signatures? I suppose they're in the file that is updated when you do an 
update. But where is this file?

Why are every file in the package md5summed ? Wouldn't a sum on the 
whole package be enough?

I had a bad experience while trying to install guarddog on Knoppix 
(installed)this weekend. Synaptic apparently did a full update before 
installing guarddog, even chinese keyboards! That took a long time! It 
was getting late and the fine print was really, really small. At one 
point it asked if I wanted to restart the computer or continue. I was in 
no mood to restart and thought "What the heck, I'll see to this later!"

When I rebooted I had the message "Starting system log daemon: syslogd" 
and the system hanged there. I rebooted with a Kubuntu Live-CD and tried 
to find an answer to this problem on the net, but in vain. So, I 
rebooted and removed savedefault on the boot prompt. The boot hanged 
very soon. I put back  savedefault, and it finally worked. Lots of 
headaches!

Is there a Linux distro that won't let you continue when you *have* to 
reboot? You know, more foolproof.

Thanks!