If you are using 3rd party all-in-one servers on windows (like Uniform Server etc), "php_soap.dll" may not be included in the default distribution. If this is the case, the do phpinfo(); first, check what compiler is used - you need to find out if it's VC6 or VC9, then got to official php download page, get windows binary distribution (.zip archive recommended), and copy php_soap.dll from that archive to your server (on Uniform it's <path>usr\local\php\extensions\ and then restart the apache service. Please note that despite of compiler difference, PHP comes in two flavours - thread safe and non thread safe. If one does not work for you (check logs - "unable to load dynamic library '...' usually means file is not there (not the case) or cannot be loaded (due to compiler ABI mismatch or ts/nts mismatch). Try thread safe binaries first.
