Upon trying to launch any version of Minecraft I get this output from the launcher:

Exception in thread "main" java.lang.NoClassDefFoundError: net/minecraft/client/main/Main
Caused by: java.lang.ClassNotFoundException: net.minecraft.client.main.Main
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)

I have Apple's version of Java SE 6 Runtime, as the latest version of Java apparently doesn't work with Minecraft.

I also must point out that I literally just bought this machine. It seems to take an obscenely long time to download the launcher files and minecraft.jar for any version selected only to fail in the above way every single time.