Debian :: Package Management - Can't Install Its Nb Pdf Reader / Fix It?

I am new to Debian but a long term user of various other Linux distros, most commonly Ubuntu at home and Xubuntu for my old work computer. I tried Debian 6 LXDE the other day on the older PC, from a live LXF disc. It picked up all my hardware automatically and was so stable (more so than the Xubuntu LXDE distro on the HD) that I decided to install it.

Now that it is on the HD it is still very stable, but I am struggling with package management and installing "stuff".

I am fairly comfortable with the CLI and have managed to get myself into the sudoers group, install grub and add the old Xubuntu to grub manually (I was not impressed that Debian didn't pick up the other two distros on the machine, even after a grub install and update grub and all the other tricks I could think of).

Anyway, back to package mngt:

First, why is there no pdf viewer/reader by default? How do you start building if you can't read the many helpful articles in pdf?

But more annoying, when I try to install pdfedit, epdfview, evince, okular, pdf-viewer, osso-pdf-viewer or kpdf (at least one of which MUST work in Debian LXDE) using "apt-get install" or "aptitude install", as root or as sudo in the Terminal, why do I get "Couldn't find any package whose name or description matched" "Couldn't find package" or "Unable to locate package"? I can't even install synaptic to help!

Then I found that my sources.lst only listed the install CD as a repository (how stupid is that?) so added some repositories to it (eg deb http://http.us.debian.org/debian stable main contrib non-free) and did a sudo apt-get update. And apt STILL can't find anything.

And what is that Debian Installer in the >Menu>System Tools? It asks for a password then nothing opens that I can detect. Is there a GUI for package mngt?