Why does every single application insist on installing a completely useless icon into the system tray? It would be one thing if it performed some function, but it doesn't do anything that you can't do from your control panel. The least they could have done is have a dialog during the setup process that says "Would you like a useless icon in your system tray?" 

Anyway, let's get to removing that Java icon… if the icon is currently visible, you can just right-click it and open the Control Panel from there, but you'll get a warning dialog when running Vista.

If the icon isn't currently visible, you can still get to the Java control panel by going to the Vista (or XP) Control Panel and looking for the Java icon. On Vista, you'll have to first click on Additional Options:

And then click on Java:

Now go to the Advanced tab, click on Miscellaneous and then uncheck "Place java icon in system tray"

Much better.

Note that the currently displayed icon won't go away immediately, you'll have to right-click and choose Hide.