I would highly recommend perusing the Smarty documentation (chm file included in sample code download). It is very well written and goes into great detail about what you can do with this lightweight but extremely elegant framework. Also, while your visiting smarty.php.net, take a look in the forums to see what kind of buzz is going around, there's quite a bit of activity and support for this system. The wiki is also great, and has a pretty impressive list of plugins for everything from dreamweaver usage to form validation. There are also job requisitions for people who need specialized work done in smarty on the bulletin boards!
All in all, I personally think smarty is one of the best ways available to begin your own homegrown cms. In many ways, you can save yourself the headache of using a pre-designed cms package and reverse engineering it down or sideways to what you need it to do. Not to balk at these packages, some of them are fantastic, and very easy to implement (one of my favorite ones out there is cmsmadesimple), or at least have some great designs that you can use bits and pieces of in your own framework. Good luck!
About Ben Robinson
Ben Robinson is an open source coder who enjoys working on dynamic web applications, especially in PHP and mysql, in the L.A.M.P. environment. His website is TierraLogic Systems (http://www.tierralogic.com/) if youd like to pay him a visit.