If you do not require Java it is best to leave it disabled in Safari and any other browser you may use.
In Safari, make Safari Preferences look like this:
Your version of Safari for Leopard may look a little different, but find the checkbox for "Enable Java" and un-check it.
Also, if you have a Java Runtime installed, disable it. To do that go to your Utilities folder and open Java Preferences.
If you see the following dialog box
... then click Not Now and you're finished.
If you see the following instead
... then un-check that box.