Problems of this sort are often related to the different environment that your web server runs the script from, vs. you the user. In particular, with Oracle, things like $ORACLE_HOME need to be set for things to work properly. Perhaps you need to set that in your script, say, in a BEGIN {} block?

Just a thought

Update: On further thought, chances are that ODBC takes care of things like that for you - that's definitely an issue when you use DBD::Oracle. I just glanced through the documentation for DBD::ODBC, and I couldn't help but notice a heading entitled 'Using DBD::ODBC with web servers under Win32.' Perhaps the info there will be of help to you?