If you want to add the Solr extension to your exisiting PHP install, you need to make sure you use the same API to build the extension as was used to build PHP or you'll get errors like:
PHP Warning: PHP Startup: solr: Unable to initialize module\nModule compiled with module API=20060613\nPHP compiled with module API=20090626\nThese options need to match\n in Unknown on line 0
To avoid this, use your existing phpize and php-config when compiling the extension (change the '/usr/local/php5/' below to whatever your existing path is.)
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/solr.
For help and support, please visit the extension google group. » Apache Solr PHP Extension
A DLL for this PECL extension is currently unavailable. See also the building on Windows section.
The solr module can be compiled in debug mode by passing the --enable-solr-debug flag to configure
When building manually, be sure to include curl and libxml support within the build.