1 - You need to install the Oracle client libs on your PHP box. The tnsnames.ora file must contain the address of the remote DB.
2 -There must be a listener running on your Oracle box in order to accept remote requests.
3 - Compile PHP with :
./configure --with-oci8=$ORACLE_HOME
to add oracle OCI support
The syntax of OCI logon is:
OCILogon(userid, password, [DBName])
ex:
OCILogon("scott","tiger","ORCL");
or
OCILogon("scott/tiger@ORCL") is a valid form.
Don't hesitate to post for more help.
JBL