So I was digging for books around the net and, just by coincidence, noticed Herbert's name on one of the titles.
Turns out it's the 92-page version of his guide to physical education. APK posted their own 30 page version, but it leaves out a bunch of chapters this one has, and sports an inferior translation.
edit: I'm told that the complete work is over 500 pages, though, so we're gonna have to hold out a bit longer for the whole thing.
The book is basically Hebert's guide to the natural method, complete with the workouts and techniques he believed every human needed in order to be strong.
And by extension, useful. ;D
Full .pdf link: http://www.mediafire.com/?e9cfazywshywts3
APK's unfinished translation: http://www.americanparkour.com/MethodeNaturelle.pdf