Thanks Simon. It's always interesting learning new languages by guess work :D
Anyway, I think this (http://devzone.zend.com/manual/ref.ldap.html) might be relevant:
"LDAP support in PHP is not enabled by default. You will need to use the --with-ldap[=DIR] configuration option when compiling PHP to enable LDAP support. DIR is the LDAP base install directory. To enable SASL support, be sure --with-ldap-sasl[=DIR] is used, and that sasl.h exists on the system.
Note to Win32 Users: In order to enable this module on a Windows environment, you must copy several files from the DLL folder of the PHP/Win32 binary package to the SYSTEM folder of your windows machine. (Ex: C:\WINNT\SYSTEM32, or C:\WINDOWS\SYSTEM). For PHP <= 4.2.0 copy libsasl.dll, for PHP >= 4.3.0 copy libeay32.dll and ssleay32.dll to your SYSTEM folder."
I've now copied libeay32.dll and ssleay32.dll into both system and system32.
And I've downloaded php-5.2.5-win32-installer.msi so now I can hopefully install PHP with LDAP support...