The zope.org web site has a good deal of information about ZPT. Recent editions of The Zope Book (an earlier version of which is also available in printed form from New Riders) include two chapters on ZPT, including examples of TAL, TALES and METAL: www.zope.org/Members/michel/ZB/ZPT.dtml and www.zope.org/Members/michel/ZB/AdvZPT.dtml.
An introduction to ZPT for Zope developers familiar with DTML is available at: www.zope.org/Wikis/DevSite/Projects/ZPT/IntroductionForDTMLers.
The specifications for TAL, TALES and METAL are short and readable and are available at www.zope.org/Wikis/DevSite/Projects/ZPT/TAL, www.zope.org/Wikis/DevSite/Projects/ZPT/TALES and www.zope.org/Wikis/DevSite/Projects/ZPT/METAL. The specifications have undergone some changes over time, so be sure to read the latest versions.