From the master node, you can start the jobtracker and the tasktrackers of the slaves. If you want to start a tasktracker separately, from this node type:
$HADOOP_HOME/bin/hadoop-daemons.sh start tasktracker
Replace start with stop command above for stopping the jobtracker and tasktracker, respectively. By the way, I think that you need to start the jobtracker, in order to see what you want, even if no tasktracker is running.