Inside the tutorial, demonstration regarding using eclipse as an editor for creating flex and ant projects is given. Also, the coding of flex and apache ant applications and compiling flex application with ant build.xml file is illustrated very nicely inside the tutorial. Along with compiling, you will also know how to execute the output file that has extension .swf with either web browser or adobe flash player, using the ant build.xml file.
Coding flex action script code on eclipse, needs java run time environment, to be installed on the system. And for using ant build tool, apache ant run time environment is required to be installed on the system.

For generating java environment visit to
url : http://www.roseindia.net/java/learn-java-in-a-day/download-and-install-java.shtml

And for establishing apache ant environment on your system visit to
url: http://www.roseindia.net/flex/downloading-installing-flex.shtml.
And for getting flex sdk visit the same above url again.

Now after all this, download eclipse from eclipse official website that has apache ant technology as an inbuilt plugin installed.
For getting the above stuff visit to
url: www.eclipse.org/downloads/download.php?file=/eclipse/downloads/drops/R-3.4.1-200809111700/eclipse-SDK-3.4.1-win32.zip

On the above url page, select any nation or continent mirror of eclipse classic. After clicking on any mirror you will get a window shown below.
On this click on ok button.