OK, first off: Linux is the name of the core of the system – like, the minimum needed to be able to run your computer. That’s not of much use by itself – you need a lot of tools (e.g. to copy files, etc.) and you might want a graphical environment, i.e. somewhere you can point and click to run stuff, like Firefox. These things are often packaged together in distributions – this is what Ubuntu is. Debian is another distribution. Thus, you want one or the other.
I’m not too familiar with Debian, but when it includes 31 disks I suppose that’s because it contains a huge amount of software, trying to fit in everything you ever might want to install. I suppose the DVD’s contain about the same – on a DVD just fits a lot more than on a CD.
I’d still go with the fancy Ubuntu CD, as that will certainly contain everything needed to set up a basic LAMP server, and then some. I suppose it’ll include documentation as well to set it up. If not on there, it at least is over here: https://help.ubuntu.com/9.10/serverguide/C/index.html
I don’t suppose it’s easy, but at least the documentation is there so you should be able to set it up if you’re willing to learn :)