Your browser will need to have a Java plugin version 1.5 or later.

If you already have a plugin installed, you can check the version by going to Sun's JVM-test page.

If you need to install a Java plugin, see Sun's plugin page, and if you are using a Netscape-family browser, also the Mozilla plugins help page.

Some versions of Internet Explorer come with Microsoft's Java Virtual Machine. But that only supports Java 1.1, because. . .never mind, just see this help page which tells you how to change your preferences from MSJVM to a later plugin.

This page is another useful source of information.