Arch
Easily the most lightweight distro ever. You basically build the entire system from the ground-up yourself. I have very little experience with it as I'm not a power user (it's absolutely not for a Linux newbie, and it can be very frustrating), but it's an amazing OS.
I used Arch on a previous laptop, and it was wonderful - and I ran xfce on it. (For my newer laptop, which is far more powerful, I got lazy and bunged Ubuntu on it, and everything works out of the box).
For an older laptop, you might also consider slackware.
-T.
Arch is only available for 64-bit hardware. It's incredibly fast because you can (relatively easily) strip everything out of it that you don't use and customize it to your own specification. But it is a high-performance distro for high-performance hardware. It's not really designed for older hardware.
Moblin has a unique desktop interface that many people like. It is designed to work well on the small screens common on netbooks. It is also optimized to run on the Intel Atom processor (Moblin is, after all, a product of Intel itself). A tool is available to simplify customizing Moblin, so that you can make it run even faster by tailoring it to your specific hardware and needs.
Puppy Linux is designed for older, lesser-spec'd hardware of every stripe. The entire distro (including most apps) loads into RAM at boot-up, so it runs remarkably fast. Some versions of Puppy only require as little as 64 MB of RAM to run, others require as much as 256 MB RAM. Puppy may be installed with either of two different windowing servers: the standard (and full-featured) X.Org or the lightweight Xvesa. A "wizard" during the installation process will examine your computer's graphics card and monitor and make recommendations as to which may be more appropriate to your specific hardware. Puppy has a unique package management tool ("PetGet") and a reasonably large repository of software from which to choose (the Puppy repository is probably bigger than Moblin's). Puppy gives all accounts root privileges (just like Windows 1.0 through XP) so it is not designed for a machine that will be shared with other people, or used by computer novices. Puppy also has a tool available to help customize the distro, so you can further tailor it to your specific hardware. You should ask trawler about Puppy, as he used to use it on at least one of his computers.
DSL "Damn Small Linux" is an extremist distro designed to run on your grandfather's computer. It is possible to get work done in DSL, but it is so minimalist that it may annoy you with its starkness. The entire distro will install onto a 64 MB flash drive - and that
includes a full suite of office apps, games, and a web browser!
Another option is to "roll your own distro," Corny. I mentioned above that both Moblin and Puppy Linux have available tools to help you modify the distro to your own requirements. Knoppix is probably the most popular distro from which to start to create a build of your own. Knoppix has available a tutorial* that walks you through the remastering process. Knoppix is a native German distro - those of us in the English-speaking world often get the updates sometime after they have been released in German. You may customize Knoppix into a small, fast, minimalist distro engineered to run well on the hardware you have available. Because Knoppix is Debian, you may benefit also from the large repository of Debian software available (Debian maintains the largest software repository in the Linux world).
You can find plenty of other tutorials on the Internet on how to customize Knoppix and other distros to your own needs and hardware, should you choose that route. You have a lot of options.
I don't know anything about the other distros you posted, Corny.
* hXXp://www.knoppix.net/wiki/Knoppix_Remastering_Howto
See also "How to Roll Your Own Linux Distro": hXXp://www.informationweek.com/news/software/showArticle.jhtml?articleID=205917063
when I was at my parents for christmas I had the images with me .. but the only thing that would boot from my USB stick was a mint image (moblin at least had the boot loader which then complained about the missing isolinux .. ) .. haha - so much for that. Of course nobody had blank CDs