The editor -is- a standalone, but it needs to have access to most of the graphics files. IIRC, installing a patch downloaded from this site may include the editor and enough things to make it go. I've used the editor without a working game on my laptop for some time, but I no longer remember whether I had to grab some graphics files from my actual Civ distro. You'll need at least terrain graphics and the units_32.pcx file. Oh, and some of the building files...