Chris Jones has a new post to his blog today showing how to use the latest 32-bit OCI8 (Oracle) drivers in a 64-bit Windows environment (like on Windows 7 or similar OSes).
The world migration from 32-bit to 64-bit operating systems is gaining pace. However I've seen a couple of customers having difficulty with the PHP OCI8 extension and Oracle DB on Windows 64-bit platforms. The errors vary depending how PHP is run. They may appear in the Apache or PHP log. [...] Other than IIS permission issues a common cause seems to be trying to use PHP with libraries from an Oracle 64-bit database on the same machine. There is currently no 64-bit version of PHP on http://php.net/ so there is a library mismatch.
The solution is to install the Oracle Instant Client, move a few files around, edit your path and you should be good to go.