Puppy Linux
My Opinion
Pros
I have switched from Damn Small Linux (DSL) to Puppy Linux as my main distro. Puppy Linux is a lightweight Linux distro (only 94 MB as of version 4.1.2). Like DSL, Puppy Linux works on many obsolete computers, can be installed in just a few minutes, and offers frugal installation (a feature that allows you to upgrade to a newer version of the OS without having to reinstall everything). Puppy Linux is much easier to use and includes a much greater selection of drivers than DSL. For example, I never could get wireless Internet to work with DSL, but I am able to get it working in seconds on Puppy Linux. I also find that the procedures needed to get things working (like printing) tend to be much more straightforward in Puppy Linux than in DSL. Also, Flash 7 and Flash 9 work from the get-go in Puppy Linux. In DSL, you have to download and install Flash 7, and Flash 9 is far too unstable to be even minimally functional.
Cons
Compared to DSL, Puppy Linux is somewhat bigger and thus uses somewhat more RAM and hard drive space. However, the key word is somewhat. DSL is only 50 MB in size and Puppy Linux (as of version 4.1.2) is only 94MB in size while most 1-CD Linux distros are close to 700MB in size. Some Linux distros are even heavier and require multiple CDs or even one or more DVDs. 256 MB of RAM and only a few GB of hard drive space are plenty for a fast and functional Puppy Linux setup but woefully inadequate for most other Linux distros. Also remember that Microsoft is the ultimate champ on bloat. In fact, the bad things I heard about Vista convinced me to switch to Linux and phase out my use of Microsoft operating systems. In other words, Puppy Linux offers much more functionality and capability than DSL for not that much more RAM and hard drive space.
Puppy Linux Procedures
NOTE: My methods aren't the only way of doing things, but they work for me. These procedures are a reference for myself. Use them at your own risk. (I recommend backing up essential files before doing anything.)
Preparation for Starting Puppy Linux: burning the CD, changing the computer boot order
Getting Started in Puppy Linux: booting up the CD, rescuing files from the hard drive, killing a process, printer setup, Internet connection
Windows/Puppy Linux Multiboot Hard Drive Frugal Installation From Live CD
PET packages (optional applications in Puppy Linux)
Changing gamma (color settings)
Installing and using WINE (for running Windows applications without actually using Windows)
Installing and using MPLAB in Puppy Linux