How to convert an Eclipse Android project to use Ant for build?
Running android update project -p . on the command line, in the base folder of your project will create the necessary build.xml and supporting files for an Ant build.
You can create ant build file directly from eclipse it self.. From File Menu
Here are the steps to create build.xml for any project in eclipse
File -> Export -> General -> Ant Buildfiles and choose required project to create a build file.
While there may be no "Run Configuration to Ant" feature you can still open the run configuration and view the settings.
The Android Developers site has a section on using "Other IDEs"; here they cover a little on using Ant to compile if you're familiar with Ant already.