If you need to configure your xampp installation (on winXP) to connect to the oracle

- first you need to download oracle basic instant client for windows

- After unzipping the instant client on a selected directory (i.e. c:/instantclient_11_1) you need to copy all dlls from this directory to “xampp/apache/bin/”

- Add instant client directory to windows system variable’s path : follow Start -> Control Panel -> System -> Advanced -> Environment Variables and edit PATH in the System variables list

- now open up php.ini from “xampp/php” and remove semicolon from this line “;extension=php_oci8.dll”

all you have to do is restarting apache and you’re all set

here is a nice document with more general detail about installing php and the oracle instant client for linux and windows