This question has appeared hidden in another thread - it's a good 'un and worth of its own thread ... so here goes

PHP is excellent glueware giving access to a very wide range of facilities, but not all of them are supported in the base PHP distribution by default.  Why?  Because you might not want / need all the facilities, and because the extra specialist facilities are best maintained by an expert in those facilities rather than by the core PHP team. By doing it this way it means you can choose to build what you want, you can upgrade your extra facilities as and when upgrades become available rather than waiing for the PHP core team, and you can run PHP on a particular OS even if some of the extra facilities aren't available there.

In the case of XSLT, PHP support is an option that you add in at build time, and it requires access to the libxslt library - whih is becoming something of a standard library and itself has an XML requirement from libxml2 ... you need both ofthese libraries pre-loaded before you can configure and load PHP with xslt support. If you look at http://xmlsoft.org/XSLT/ it'll get you started ... and once you've got xslt installed and running (use xsltproc to test it?) you'll be able to get on to PHP

When you (re) build your PHP, you'll need so specifiy the --with-xsl option when you run the configure command.   Here's the details, gleaned from a PHP5 build system I have around at the moment  
Code:

[trainee@pasanda php-5.0.0RC2]$ ./configure --help | grep -i "xsl"  --with-xsl[=DIR]        Include new XSL support (requires libxslt >= 1.0.18).                          DIR is the libxslt install directory.

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