The HttpResponse class requires at least PHP v5.1. Any other class is available as of PHP v5.0.
Note: Be aware though, that some methods are not available with PHP v5.0.
Installation requirements on Windows
Installation requirements on other platforms
The extension must be built with » libcurl support to enable request functionality (--with-http-curl-requests). A library version equal or greater to v7.12.3 is required.
To enable support for sending and receiving compressed responses, the extension must be built with » zlib support (--with-http-zlib-compression). A library version equal or greater than v1.2.2 is required.
Content type quessing can be enabled by building this extension with » libmagic support (--with-http-magic-mime).