What I want to do is create an apt respository for two or more computers. However, I want one of these computers to serve the packages. Furthermore, I want the server to be able to grab the most recent updates for Sid and be able to provide those packages.

I'm using Debian Sid on a couple of computers. Since I'm not using a fast connection, it would be an annoyance to use "apt-get upgrade" on all of the computers. Therefore, I want to keep one main computer on at all times. This main computer will check for new packages and download them.

The only problem with this logic, however, is that different computers (different hardware, etc.) with Debian Sid may have different packages installed. Therefore, the server computer would only download upgrades to its own packages. At least, that's the experience I've had with making my own repository.

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I want to find a way to give the server a list of packages that exist on client computers and itself; afterwards, I want the server to download upgrades (if they exist) for those packages. After that is accomplished, I want these packages to be put into a local repository.

From there, I should be able to use a client computer to access the server's local repository and locally download any existent package upgrades.

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I have tried to mirror a Debian repository before, but it didn't work so well. For some reason, the computers thought my repository was not a mirror of the Debian repository. For instance, I would have my repository and the Debian repository in the sources.list. The computer, however wanted to download things from the Debian repository instead of my repository: I had the impression the computer thought my repository was impure and *somehow* not the same. I didn't understand why my packages weren't seen as the same as the Debian repository.

I wanted the repository to appear the same, because that would mean the clients wouldn't have to download as many packages if they already existed (as installed) on the server computer: The ones that did exist could be transferred more quickly than being downloaded over the Internet.

Because if I had a server that downloaded stuff like LaTeX and Openoffice packages from Debian or its mirrors, then I could create a local repository mirror and provide it to my client computers.

How do I do what I want to do?

You should be looking at apt-pinning. In this case, you would pin your repository higher than the debian repositories. Also, apt-mirror may be useful here too.