Copy it and overwritten the original android_rules.xml under ${ANDROID_SDK}/platforms/android-1.5/templates/ directory.
This build file should work both on pure-Java source code and Scala source code mixed with Java source code, if your android application is written by Java, just run ant debug/reinstall/release as usual.
If your android application is written in Scala, then you need create an tools directory and copy both scala-compiler.jar and scala-library.jar into it like Step 3 in chris blogs.
Now, run ant reinstall to test and enjoy your Scala-powered Android application.