You're in luck, I've been working with LDAP for the past two years at my college. We've been using Java instead of PHP, but I understand how LDAP works pretty well.
You have two options. First, as was mentioned, was OpenLDAP. The problem is that it only works in Unix enviroments. That means trying to get it to work via Cygwin (
www.cygwin.com). Cygwin is a very nice Unix emulation program for windows. While it isn't as good as the real thing (and I strongly suggest getting a Linux box for this), it's a good workaround.
Or, if you want something a little easier to handle, Sun has their own LDAP server(
http://wwws.sun.com/software/product...directory.html). That's the one we use at the college, and have been using it ever since it was Netscape's LDAP server many moons ago. It has a nice UI to it. It's only trial software though (we at the college have the liscenced version), and it claims to require Windows Advanced Server SP2. But try it and see if it works on whatever you're using.