Here's how I'm building crosswords for Android.

First, the build process requires a file called local.properties that
must be generated locally.  Generate it before your first build by
running ./scripts/setup_local_props.sh.

The working directory is XWords4 within this (android/) directory.
Run the following commands from there.

Build the jni library (the cross-platform code):
# ../scripts/ndkbuild.sh 

Then build the app for the emulator (assuming it's running)
# ant debug install

Build for a device (requires you've set up your keys.  I did this too
long ago to remember how but the info's easy to find):
# ant release
(The above command not yet verified for new SDK I installed on 11/19/11)