PS here's the Oracle note on how to convert your database character set:
http://metalink.oracle.com/metalink/plsql/ml2_documents.showDocument?p_id=66320.1&p_database_id=NOT
Quick summary: alter database character set UTF8;
Beware the dreaded ORA-12712: new character set must be a superset of old character set!
As I said your data is probably screwed, so there's no point running the conversion until you clean it up.
