A. Licensing for VMware ESX's features has always been by the individual host. This fact has, at times, caused a bit of confusion among administrators who see its per-processor pricing and license assignment. While you'll absolutely purchase ESX licenses on a per-processor basis, those servers' actual features are always centered around the host itself.
VMware HA and DRS are two features with licensing that commonly gets confused. That's because HA and DRS are available in different editions of ESX, even though their configuration appears in the same place inside the vSphere client management tool. For ESX 4.1, VMware HA is available in Essential Plus, Standard, Advanced, Enterprise, and Enterprise Plus editions. VMware DRS for vSphere 4.1 is only available at the Enterprise and Enterprise Plus editions.
Figure: Licensed Features.
An easy way to determine whether you've got the right edition is to select a host in the vSphere Client and then navigate to Configuration, Licensed Features. As you can see in the figure above, this link will display the list of features enabled for the currently-selected ESX host. Note in the figure that this host is enabled for both VMware HA and VMware DRS.
Catch up with @ConcentratdGreg on Twitter!