Linux Lite: Small distros for old machines

One of the reasons why one would get Linux is to make use of old hardware. Windows Vista, with all the DRMs built in, is bloated beyond belief, especially with the shiny "Aero" effects. Pretty but useless, like Paris Hilton... Anyways, people who do this had better check the system requirements before they pick a distribution. Ubuntu is the obvious choice for most people, but when that person is stuck on a 400MHz Pentium II laptop with 128MB of RAM, it might not be such a good idea. So, here are some small distributions that get the job done on old systems, too. They might also be good for gamers who want to eke every possible bit of performance out of their machine.
-Ubuntu Lite and Fluxbuntu: Variants on Ubuntu that use IceWM and Fluxbox, respectively, as their desktops. Although these are lighter than their GNOME counterpart, you can still do better- they come with bloated services that slow the system down.
-Damn Small Linux: "50 megabytes of penguin power", a business-card-sized CD that runs Fluxbox and a collection of tiny apps. With a 2.4-series kernel, hardware compatibility will be limited, but it works fine for gaming.
-Zenwalk: Slackware is incredibly efficient, but hard to install. Zenwalk is a friendlier distribution based on Slackware, but using XFCE, which also runs faster (but isn't too hard to use).
-Absolute Linux: Absolute is a lightweight desktop (it boasts an idle RAM usage of only 26MB with certain services disabled), but the CD comes with an enormous number of programs. It uses IceWM, and is based on Slackware.
-DeLi (Desktop Lite): A small, independent distribution. The CD image is only about 130MB, and it is designed to run on really old machines- it can run on 8MB of RAM. Also uses IceWM.
-PCLinuxOS and SAM Linux: Although they're not as small as the previously-mentioned distros, these forks of Mandriva run superbly on relatively old machines (my test system, in case I need to remind anyone, is an 800MHz Celeron with in i810 graphics chipset and 320MB of RAM). PCLinuxOS uses KDE, and runs faster than Ubuntu. SAM uses XFCE, and has a great, OSX-like launcher. PCLinuxOS is currently the top distribution according to DistroWatch (surprise!).

When looking for a fast system, there are three things to keep in mind:

• The desktop. Most lightweight distributions use either XFCE (gaming systems) or IceWM (legacy systems). IceWM is *tiny*, but XFCE is a complete environment, with its own apps and libraries.
• Bloatedness. Distros like Ubuntu or openSUSE (and especially Fedora) have a lot of services running in the background, and they slow the whole thing down. Distros that follow a strict KISS (Keep It Simple, Stupid) strategy (Slackware and the like) don't have all this bloat slowing them down.
• Optimizations. Distros like PCLinuxOS are optimized for an i586 (Pentium) or later CPU. This means they won't run on a 486 or later, but they'll run extra-fast everywhere else. Arch is i686-optimized (Pentium II), the highest level, and follows KISS (which has nothing to do with Gene Simmons). Gentoo and other source-based distros let you choose how you want it optimized, but are notoriously hard to install.

Finally, as a general consideration for making your system even lighter (and snappier), make sure you're not loading any more libraries than you need to. Here's an example:
A normal system:
-GIMP (uses GTK)
-Firefox (uses libFirefox)
-amaroK (uses Qt, KHTML)
-Nautilus (uses GTK, libGNOME)
-arK (uses Qt)
-Tomboy (uses GTK)
...You get the idea. The apps on this system either load too many libraries or rely on their own. A good system uses a couple libraries a lot.
Optimized system:
-GIMP (uses GTK)
-Epiphany (uses GTK, GTKHTML)
-Exaile (uses GTK)
-Thunar (uses GTK, Exo)
-XArchiver (uses GTK, Exo)
-Orage (uses GTK, Exo)
Three libraries are shared between 6 programs, which would otherwise be packing their own libraries.
From SAM Linux 2007,
The DistRogue.