I had the chance to start playing around with the new PHP5 Soap Extension the other day and was dissapointed on a couple fronts:
1. If you use a WSDL file you cannot manually set an endpoint, so endpoints are directly tied to a wsdl file. Works for most maybe but at the enterprise level when you're distributing applications the endpoint could be in a configuration file to point to somewhere local in the network. NuSoap supports this feature.
2. The Soap Extension does not support generating a WSDL for you, NuSoap supports this feature
Hopefully as time passes we'll get these two things implemented to make the Soap Extension more enterprise ready. I have yet to test it with .Net services but I'll give that a whirl soon.
Here are some tips on getting the soap ext working with Windows:
to get php5 soap running under windows you need to add this line to php.ini in the extensions section extension=php_soap.dll
and make sure the extension exists NOTE: soap ext and nusoap do not get along because they share the same class name soapclient so you have to run one or the other, not both