This download does not include the Java Runtime. You will be prompted on startup for the path for the JRE. The minimum is JRE 1.6.
SQL Developer Data Modeler is supported on 64-bit platforms, ensure you use the 64-bit executable available in the zip file. If you use the 64-bit Data Modeler executable, you will need to use a 64-bit JRE.
To install and run: