I have seen different results with different browsers. Chrome, and Firefox version 15 and earlier seem to work best. Which browsers have you tried?
Chrome, Safari (6.0.4), Firefox (20.0).
However, I've had no issues with actually downloading the jviewer.jnlp and executing it. Java 7 (64-bit) starts up fine; it just doesn't work consistently.
I've been reading that some people have had success with the CD-ROM feature only on Java 6 32-bit. However, since I'm running on a current Mac OS X I have no real options for downgrading my Java 6 to 32-bit, since Java 7 is required for a lot of my other management applications and Oracle does not make a 32-bit version of Java 7 for Mac.