java.lang.ClassNotFoundException: API WebDriver

Я скачал selenium-java-2.0a5.zip

http://code.google.com/p/selenium/downloads/list

и запустил следующий код:

package org.openqa.selenium.example;

import org.openqa.selenium.By;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.htmlunit.HtmlUnitDriver;

public class Example  {
    public static void main(String[] args) {
        // Create a new instance of the html unit driver
        // Notice that the remainder of the code relies on the interface, 
        // not the implementation.
        WebDriver driver = new HtmlUnitDriver();

        // And now use this to visit Google
        driver.get("http://www.google.com");

        // Find the text input element by its name
        WebElement element = driver.findElement(By.name("q"));

        // Enter something to search for
        element.sendKeys("Cheese!");

        // Now submit the form. WebDriver will find the form for us from the element
        element.submit();

        // Check the title of the page
        System.out.println("Page title is: " + driver.getTitle());
    }
}

но потом я получил

    at org.openqa.selenium.example.Example.main(Example.java:13)
Caused by: java.lang.ClassNotFoundException: com.gargoylesoftware.htmlunit.WebWindowListener
    at java.net.URLClassLoader$1.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    ... 1 more

Я пропустил шаг? Я удостоверился, что импортировал selenium-java-2.0a5.jar в проект.