I've copied all files to /limesurvey/ on my local server but when I go to /limesurvey/index.php it loads the first two screens and begins pre-installation checks. The screen tells me that "PHP PDO library" is "Not found".
I've copied the php.ini file to the base folder and enabled the extensions. (JSON and mbstring extensions where recognised before I did this)
Is there something simple I haven't done as I don't have problems with other sites using the current php.ini settings?

PDO is furnished with PHP since php 5.1
PHP 5.3 is the minimum required for LimeSurvey.

Yes I know that. I have PHP5.5.24 installed with php.ini file located in the base directory of limesurvey . The installer is not recognising it while it recognises mbstring and others required.

Ok, so basically, you resolved the problem ?
I'd say it must come from your server configuration. PDO should be available with any version of PHP superior to 5.1.
Also, we could add a check for PDO like we're doing for other libs, but that would be to cover some exotic server configurations...

Whatever : thank you for reporting.

Sorry Louis I may not be expressing myself correctly. I still have the error. I cannot install Lime Survey because the pre-checks say that 'PHP PDO library' is not found when it is installed with PHP5.5. What I'm asking is, has anyone had the problem or know how to fix it? I'm stumped! I've tried searching the web, forums and IRC for clues to what might cause the installer to not recognise what is there. So far I have had no success at correcting the problem. I've removed the ';' from the php.ini file but the installer refusing to recognise it.

Found the problem. Server was pointing at the wrong php.ini file. My error!