After Macintosh and Windows, I installed FC6 on a dual book laptop and am very happy with the installation. I would like to install another Linux distro on a desktop machine, however, the goal is not simplicity, but quite the opposite: I'd like to install a distro that is completely different from FC6 and that will force me to learn a lot more about Linux. This could include different program installation systems, different command lines, etc. I would like to get a well-rounded feel of what Linux is all about, and to feel comfortable when using any distro. I've only been using Linux for a few weeks, so I'm not sure what I'd be looking for and what the actual differences are from one distro to another. I know that the 'yum' system doesn't exist in all distros, and would like to learn more about scripts. In addition to it being very different from FC6, I would like it to be a free, high-quality distro. I'd be using it with Windows on another dual boot box.

I would appreciate any comments from any experienced Linux users who have a good working knowledge of different distros.

Cheers.

I would suggest checking out gentoo, slackware, linux from scratch, and arch. Those are as far as I know are going to give you what you are looking for. You can check them out on this forum and also look at there own sites.

I hope that will give you a place to start, enjoy your quest.

Gentoo - http://www.gentoo.org/
Slackware - http://www.slackware.com/
LFS - http://www.linuxfromscratch.org/

Slackware:
http://www.slackware.com/

Does anybody know which Linux distros are generally used in universities and research centres?

Not sure, but probably the like of Red Hat, Slakware, Suse.

I know I've seen a research centre working in AI using Fedora Core. Not sure what version, though.

I know one university, in the computing lab, all the machines dual boot Windows 2000 and Slackware 11.0

I have worked with RedHat Linux, Fedora Core, SuSE, early Slackware ... I finally ended up with Gentoo.
Reading the Handbook to install the OS gave me information that I did not get when a GUI installer (note that Gentoo also has one) is used.
Manually editing configuration files gave me understanding of what the OS is doing and how I can customize it.
I keep learning more every time I run into a problem that needs to be solved ... ie. adding a wireless usb device.

I now run Gentoo on a desktop PC, two laptops, and within a Virtual Machine on my Windows box.