Assuming you have the thread safe version of PHP 5.5 32bit, you can download the 2.0.4 library from here:
http://sdk-snapshots.couchbase.com/php/php_couchbase-2.0.4-5.5-zts-vc11-x86.zip
Which is found on this page:
http://docs.couchbase.com/developer/php-2.0/download-links.html