In order to using oralce functions in php. you need to install oracle client. then copy the necessary dll files(depends on which module you are using, oci8 or oralce) to win(nt)/system(32) folder.
If you use NT, you can setup some Environment Variables like ORACLE_HOME, ORACLE_NLS/NLS_LANG. Elseif you are using win 95/98/me, you can set them on the coding[putenv();]. Also you need to set ORACLE_SID in your coding. it's for the db_address and it has to fit one of your record in tns file(under oracle client). i think this should get your php able to run and connect to oracle.
about the perforamce problem, if the DB is not on intranet, it should be slow. so you better prolong your exectuable time [set_time_limit(600);] in your coding.
Hope this helps,
kim