LDAP to SQL Express 2005 via PHP?

Okie Dokie...I have been working with MySQL and PHP for years, and now I have hit an issue & I have no idea where to start. Please be kind if this is not the right forum. I have an eCommerce site that I purchased which runs on Windows 2003 server and uses SQL Express. I need to write a php web-service that will allow me to update that table. I run my php stuff on an UBUNTU (LAMP) server. It was recommended to me by the software manufacture that I could use LDAP to make this happen...But, despite all my reading, it just doesn't make sense to me. Does anyone have at the very least an idea of how I make this work? I guess I am looking for a starting point. Thanks in advance!