Hi, well first, to solve this problem you need to take a more stepped approach.

First, make sure you can get the webservice to work for you, completely, and then worry about the third party with the PHP page.  You'd be surprised how many PHP have no idea how to interact with webservices, so you may be against a technical challenge there even if your webservice was the best thing since sliced bread. 

Due to technical limitations of your client, you may want to consider possibly building an httphandler instead, and then having them hit that instead passing request parameters as appropriate....lots of time PHP people are a bit better with that sort of basic tech.

None the less you need to make sure your enviroment works perfectly fine before you involve your client. In this case you should build a seperate website perhaps that consumes the service you built, and pass your own tests to it.  If you do this all in one solution you should be able to easily step through the code to see how things are going.

Also, if you expect XML from someone else, you may want to learn how to build an xml validator that way you can validate the xml your receiving.  You can never assume the client is going to pass you something appropriate...users always do what you don't expect.