Make sure you know what your oracle home directory is. On Linux you can test for it using
set | grep ORACLE.
As long as that's set correctly, there's no need to specify --with-oci8=<some directory> since the default will be ORACLE_HOME. Notice I'm not using --with-oracle but rather --with-oci8. Don't use both at the same time. The "--with-oracle" directive is for Oracle7, not 8 or 9 which people generally have.
My PHP 4.2.3 that worked configure script is ./configure --with-apxs2=/usr/local/apache/bin/apxs --enable-so --without-mysql -with-oci8
Finally, make sure to set the ORACLE environment variables in our apachectl file, which starts up httpd:
export ORACLE_HOME=/opt/oracle/product/9.0.1
export LD_LIBRARY_PATH=$ORACLE_HOME/lib
Please replace the ORACLE_HOME with what your ORACLE_HOME actually is.
And finally, On LInux I place the ORACLE library directory in /etc/ld.so.conf as
/opt/oracle/product/9.0.1/lib
and run ldconfig