Paul,
I had problems with the php_oracle.dll module as well. How I remedied it was I used the php_oci8.dll (download.swwwing.com)instead.
Make sure that you install the Oracle client on you system, or the dll won't run. Also, make sure that the Oracle client path is valid in your autoexec.bat, or it won't work (speaking from experience ;-) ).
I downloaded all of my extensions from some German site, and it had in it a cool test page called extensions.php. Unfortunately, I can't remember the site. I ran this page to make sure all of my extensions were up and running. If you want, email me and I'll send you the page.
Cheers,
Jason