Please read the reply on the following discussion: Migrating MS Access to Oracle 11gR2
It seems that SQL Developer 3.2 with JDK 1.6 may be your best alternative for now.
The bugs logged in this area during the SQL Developer 4.0 development cycle are generally marked as "Closed, not feasible to fix" and at least two have comments to the effect that:
odbc-jdbc has been removed from JDK7
We are in talks with Java team to source alternatives
Unsure if any progress has been made with respect to sourcing an alternative.
SQL Developer Team
P.S.: Not sure if the following is the latest word on this or out-of-date: JDBC-ODBC Bridge