How can I get Zabbix to display the same item from multiple hosts in a single graph? I wish to compare the item on different hosts.
You can create a custom graph that pulls items from multiple hosts. The graph however will be associated with a host, in which case you could create a phantom host which you can associate the graph with.
Alternatively there are aggregate hosts available as well. These allow for the accumulation of items across all hosts in a host group.