To install, you just extract the palemoon folder to the area of your choice; if upgrading, you can extract it over your existing New Moon folder. All of your settings and extensions will be maintained, and the browser will recognize an upgrade on first start. @i430VX has also made an installer for New Moon.
There seems to be two separate branches of PM: v27 and v28. I guess the former is to allow the use of extensions that are incompatible with v28.