For an old computer with a P3 955 MHz processor and 128 MB RAM, lightweight Linux distributions are recommended to ensure smooth performance. Options like Damn Small Linux (DSL), Puppy Linux, and VectorLinux are particularly suitable due to their low resource requirements. While Ubuntu is user-friendly and has good hardware autodetection, it may not perform well with the limited RAM, especially when using heavier desktop environments like KDE or GNOME. Instead, lighter desktop environments such as XFCE or Fluxbox are advised. The choice of Linux distribution ultimately depends on specific needs, such as ease of use versus performance, with no single "best" option available. Upgrading RAM to 512 MB or 1 GB could allow for more flexibility in using desktop environments, but processor limitations should also be considered.