I am currently running Red hat 9 which apparently is out of date so i'm changing. I'm in the process of downloading Ubuntu, is this a good version to start learning linux with?

also (this is probably a really stupid question) how come some distributions have like four install Cd's yet some (like ubuntu) appear to have only one?

ubuntu is fine, yes. ubuntu has one cd only because it comes with less software to install on the cd... simple as that. it can hook into debians online apt-get repository where there are thousands of packages.

Any distro is good for learning, but some distos are better suited for certain types of learning.Basically there are three types of distros (there are many ways of classifying distros , but I think this is a sensible one considering your question):
RPM based - RedHat, Fedora, Mandriva, Suse, etc.
Debian Based - Debian, Ubuntu, etc
others - Slackware, Gentoo, etc.

In all distros you can compile programs from source, but in many disros you can also download the precompiled binaries in some package format (rpm for redhat-like distros, .deb packages for debian based distros, and there's more).
The advantage of precompiled packages is that usually they also include a system to make dependency detection a lot easier + there's aften an installer available that will get the package + dependencies for you from any repositories you may have set up for your system.

As for distro choice, if you are familiar with RedHat, the most logical 'update' might be Fedora. Ubuntu is fine, it's just from another 'branch'. Both are relatively easy distros as far as installation and configuration are concerned. If you want something more challenging (although there's quite some challenge in any linux system if you want it) there are others, like Slackware and Gentoo.

The reason why some distros come with just one cd and others with as many as 5 is that not all distros include so many additional packages with the installation disks, although in all cases you can get everything that's on the cds and more from the distros repositories. This has advantages and disadvantages. If you don't have constant access to a good internet connectiomn it may be handy to get as many apps from a cd as possible. If you are on a fast cable link, downloading lots of packages from the ointernet repos is easy and the need for cds is greatly reduced.

I started Linux with Knoppix- which I've heard is a harder dist. to start with. I've found, thought that it makes me work harder to figure things out, so I learn more, faster.

thanks for input guys but this has raised another query... Debian based? RPM based? OTHERS? i'm confused!!

Those are all types of packages and package managers, meaning, you can download and install software with a siple command (very handy). Foor instance, on Fedora, #yum install <app> will install <app> from a repository on the internet. #apt-get install <app> will do the same for deb based systems. Gentoo (one of the "others") relies on a portage system--#emerge <app> will custom compile <app> on your computer. Check the individual websites of each distrobution to get more information.

an excellent online book which is really easy to follow, and easy to understand is

rute

it helped me greatly when i was starting out. it is (or was) based on rpm based distros, but now covers almost everything about getting started...