I'm new to PHP too, but I believe you need to install and setup SQL*Net/Net8 on the same machine where PHP resides. You only need this client side protocol to talk with your Oracle database - don't install the whole Oracle server!
To configure it, you need to edit the tnsnames.ora file - usually in $ORACLE_HOME/network/admin (Unix side) or some similar location on NT.
The file itself contains the means to define network services so that your client programs (i.e.PHP) can find the Oracle database by a simple name. You need to create a new entry by copying a tcp/ip entry and then changing the name, global_name, hostname and SID/service value for Oracle.
I hope this helps!
Regards,
Rick