I try to run http://www.chess.com/play/computer.html and Rybka 2-cores, but it shows as 4 cores so running java too makes the http://www.chess.com/play/computer.html crash, it worked at first, but ever since I have had problems. Is it Java's fault?

If you're running Windows....

start /control panel/java/advanced/miscellaneous/check box "Place icon in system tray"

Also try clearing your cache, and even your java cache. see: http://www.java.com/en/download/help/plugin_cache.xml

Then try 'against the computer'.  If you're still having issues come back to this thread and let us know.  :)

I found the issue. My chess program had "Ponder" on, and taking it off my computer could use CPU on the java without disturbance, as these online chess programs uses our CPU.