I assume you are using Lion and not "10.5.7" indicated at the bottom of your message?
For what it's worth, here is what I do. I have a Java applet that I use maybe a few time a week. Before opening the applet, I open Java Preferences (/Applications/Utilities/Java Preferences.app) and tick the "Enable applet plug-in…" box. Then I run the applet. Then I untick the box. I don't forget, because I leave Java Preferences open until I am finished. No need to restart Safari or anything.
Thanks JJ2 & MrH, though I was already using that Safari plug-in toggle.
My problem is forgetting to switch it back off once I've needed to use the Java plug-in for some task. I use "control+option+command+eject" to go straight to shutdown in a single step (a life-style decision:), so even if I've got the Java Preferences open it doesn't help me. So I was wondering if there's a "Start Up task list" somewhere on Lion (thanks for the prompt about my silly OSX version number, MrH) where I can insert a simple script to toggle it back to "off" upon start up.
Using information from this Java web plug-in article (read all the comments there, for the details and updates, and for the warning about the quotes characters "fun" lurking there) and the login items for your user (System Preferences > Users & Groups > Login Items) and a little custom coding can probably get you to where you want.
That particular script describes how to enable Java, and you're aiming to disable it; there'll be some tweaks needed.
And FWIW, it was Jeffrey Jones2 that pointed to the version number; not me. That particular bit of data is retrieved from your settings here in the forums.