Here is how to do it if you use Internet Explorer:

Internet Explorer 4.x and Up

1. Click "Tools" --> "Internet Options"
2. Select the Advanced Tab, and scroll down to "Java (Sun)"
3. Check the box next to the Java version
4. Next, select the Security Tab, and select the "Custom Level" button
5. Scroll down to "Scripting of Java applets"
6. Make sure the "Enable" radio button is checked.
7. Click OK to save your preference.

Here is how to enable Java if you have Firefox:

Other Web Browsers Firefox 0.8 and Up

1. Start Mozilla Firefox browser
2. Select Tools > Options.
3. Dialog box: Options
4. Click Web Features > Select Enable Java


More help: http://www.java.com/en/download/help/enable_browser.xml