I have Oracle 10g with SQL Developer 3.0 on Windows XP, they worked well untill I just installed Oracle ODBC (ODAC101040.exe). I started to receive error message "no ocijdbc11 in java.library.path" and I am no longer able to use SQL Developer.
Check on the envirnment variables on the windows. Once you installed the "Oracle ODBC" it might have replaced the Old env. variables that can found in XP "System Properties> advance tab> environment Variables". Make sure you have the right environment variables that point to right directory locations. Update us with your findings.