Pablo,
In reading my PHP book, I'd be tempted to say that if you can work with the Oracle 9i database using the Oracle 8 interface library, that you might be able to make it work.
(Remember that PHP has the ora_ functions for versions 7 and 8, and then the oci functions for Oracle 8 libraries with support for LOB, FILE and ROWIDs)
This is just a guess. I'm using 8i and have no plans to upgrade to 9i. I guess it depends on the client software you have installed on your webserver and if it's backwards compatible with 8i.
Good luck and let is know how it goes.
--Joel