If you have no experience with Eclipse at all, you'd better first learn its usage on Java development. There are many resources on the web for Eclipse from quick starts to advanced uses.
After you know how to setup an Eclipse Java project for the example code of this turorial, highlight build.xml and right click on it, select [Run As] -> [Ant Build...] as below:
Then a dialog should appear, make sure to use a JRE of Java 6, as shown below:
Then click [Run] button and you'll get the same output as running Ant from the command line.
