A few references to to helpful information.
The Forth Programming Webring
starting at currently a yahoo.webring :
The Comp.Lang.Forth Newsgroup
where all forth system implementors are. The newsgroup archive is a very useful resource. From time to time, people extract some relevant information, e.g. at the sourceforge' comp.lang.forth.repository or Peter Knaggs' Forth Research Page
The 4TH tutorial
A very good online tutorial - 4TH is an ansi-forth compatible forth system, so the tutorial should work fine for PFE users too. see 4THtutor
Taygeta Forth
Taygeta has taken over much of the work what FIG' should have been for - it will provide you with a lot of information about forth, and the ftp-space hosts about every piece of free forth snippets you can find. see
Koopmann's Stack Computers
The book is a little older and definitly not for newbies but it still serves as good reference to stack computer theory. see his website and download the book.
Structure And Interpretation Of Computer Programs
a more general book : ISBN 0-262-01153-0 (MIT Press hardcover) : ISBN 0-07-000484-6 (McGraw-Hill hardcover)