If you want to use SCA to consume or produce Web services then you need PHP 5.2.0 or later, built with the soap extension enabled. If you just want to use local components, and do not wish to use the Web service bindings, then this version of SCA for PHP will also run with PHP 5.1.6.
SCA is packaged along with SDO in one combined package on PECL. See http://www.php.net/sdo#sdo.installation for installing the SCA_SDO package from PECL. The SCA code must be on the include path of your PHP installation, for example if it is installed as /usr/local/lib/php/SCA, the include_path directive must include /usr/local/lib/php