I think all Sun vouchers last a year.
Regarding the Java version, my assignment says:
Throughout this exercise, you must use exclusively the Java 2 platform. You may develop your code using any implementation of the Java 2 platform, but the submission that you return must have been tested and shown to work under a production (not development) version of the Sun Microsystems' Java 2 platform and that platform must not have been superseded by a new production version for more than 18 months by the time you make your submission.
You are permitted to use any IDE tool you choose, but you must not submit any code that is not your own work. The final program must have no dependencies on any libraries other than those of the Java 2 Platform.