Setting up is as for any other custom Antlib. You need a <typedef/> and a namespace declaration. After that the custom Task and Types are available in the defined namespace. If you put the calabash.jar to your Ant classpath, e. g. by placing it inside ${ant.home}/lib, you can even save the <typedef/> declaration ant the namespace definition is enough to invoke the secret magic that automatically loads the Antlib as soon as it is used in the build file.

<project xmlns:c="antlib:com.xmlcalabash">
    <typedef uri="antlib:com.xmlcalabash"
             resource="com/xmlcalabash/antlib.xml"
             classpath="path/to/calabash.jar"/>
</project>