Actually, there *is* a DLL available for download on Windows from PECL package page, since Apr-2012.
This » PECL extension is not bundled with PHP.
Information for installing this PECL extension may be found in the manual chapter titled Installation of PECL extensions. Additional information such as new releases, downloads, source files, maintainer information, and a CHANGELOG, can be located here: » http://pecl.php.net/package/yaml.
A DLL for this PECL extension is currently unavailable. See also the building on Windows section.