In the next to last article of their loader series, DevShed looks at replacing some of the file loading functionality in their examples with functions from the SPL.
As I mentioned before, the Standard PHP library comes bundled with some helpful functions, such as "spl_autoload()," "spl_register_extension()" and "spl_autoload_register()" that allow you to either use a default implementation of the "__autoload()" function, or create a custom one for it.
Their example defines the extensions to use for autoloading and the name of the file/class to pull in. The rest is done automagically.