I am trying to get the Java applet found here: http://phet.colorado.edu/en/simulation/molecule-shapes to run. I'm running Mac OS X 10.8.2 and Java SE 6 version 1.6.0_35-b10-428 (according to Java Preferences). If I click the "Download" button, a 5.7 MB "molecule-shapes_en.jar" file is downloaded. When I open it, it opens up JavaVersionChecker and I just get this: and it stays like that until I quit JavaVersionChecker. If I click the "Run Now!" button, a 1 KB file is downloaded and when I open that I get each of these in succession for about half a second and then nothing: Any ideas on how I can get this to run? Also, what is the difference between the .jar and .jnpl filetypes? Thanks!