Option 1: Start with a general-purpose distribution like Debian or Gentoo and install a lightweight desktop environment like ?xfce, ?lxde, ?icewm, or ?awesomewm

Option 2: Use a purpose-built desktop distribution for old hardware. Linux.com, DistroWatch, Google. Most of these are packaged as Live CDs, enabling easy testing without burning using ?VirtualBox. Some interesting distributions which I plan to evaluate in this way are Puppy Linux, DSL