PAMM Install Links
PAMM (Planetary Annihilation Mod manager) is a program which manages Planetary Annihilation mods, and is highly recommended. One nice feature is its ability to install mods via web links. If PAMM is installed, clicking on an install link on this site will open PAMM, and automatically install the mod.
Registry of the pamm:// scheme on your computer is done when PAMM is installed (on windows at least). If on linux or mac, you may have to jump through some extra hoops to get pamm:// links working.