in the snoopy-archives are maybe some subfolders first, because he created it as scenario-playable mod, so the you can install the terrain-mod permanently in this way
1. search for "terrain"-folder in snoopy's archives
2. copy the terrain-folder to "...\Civ3\Art" or if you've installed an addon to this "...\Civ3\Civ3PtW\Art" resp. "...\Civ3\Conquests\Art"
3. try it, it should now be available in all older savegames too, but not in sceanarios/mods with own terrain-folder