Hi Neil,
You can simply use a tSystem component. This component allows you to execute any system command. Just print the computer name with an echo, and use the parameters of the tSystem to catch what this command returns and output it into a column in the component.
java.net.InetAddress.getLocalhost().getHostName() or java.net.InetAddress.getLocalhost().getCononicalHostName() will also get you the host name for the machine running the job.