Sounds to me like the version of PHP you're using does not have Oracle database support built in. Thus, the Oracle-related functions are unavailable.
To enable Oracle database support in PHP under Windows, you need to obtain the extension DLL (php_oracle.dll), place it in your PHP directory, and then add "extension=php_oracle.dll" line to your C:\WINDOWS\php.ini file.
If you're trying to access an Oracle 8 database, you should get the php_oci8.dll file instead (in which case you should also use the OCI* functions in PHP, not the ora_* functions).
The only place I know of to get the extension DLL's not included with the Windows distribution is from http://download.swwwing.com/php4/modules/ . Unfortunately, I've heard that some people have problems with these.
Anyway, they're worth a shot. Give it a try and let us know how you go!