We're using Linux/PHP/Oracle8i here at work. In order to successfully build PHP with OCI8 support, I've found it necessary to perform a FULL Oracle install on the PHP box prior to building PHP. The reason for this is that you need to have the $ORACLE_HOME/rdbms/demo directory. I can't tell which particular portion of the Oracle install owns this directory, but this contains several important files, like oci.h
This sucks royally when your web server(s) isn't the same box as the Oracle server, but it's the only way I've found around it. Oh, and unless you like editing Oracle config files by hand, you'll want to have X installed so you can use the netasst tool to build your tnsnames.ora, etc.
