I always have to look up how to do this, so I'm going to capture this now. If you ever need to make a NAnt script branch based on the machine it's running on, here's an easy way. First, go and get the machine name that the NAnt script is running on:
<property name="machine" value="${environment::get-machine-name()}" />
Then use the if and call tasks to call another target named after the machine:
<if test="${target::exists(machine)}">
<call target="${machine}"/>
</if>
Then simply create a separate task for each machine name like this:
<target name="TEST-SERVER">
<property name="database" value="invoice_test" />
</target>
<target name="PRODUCTION-SERVER">
<property name="database" value="invoice_prod" />
</target>
We use it occasionally in build scripts to handle differences in developer workstations (try not to do this though) and server environments without forking the build scripts.