Script to count total amount of Memory allocated to VM's on each ESX host

Hi,

I am looking for a script to add up all of the RAM allocated to VM's per ESX host in vCenter.

I can quite easily display the MemoryUsageMB and the MemoryTotalMB but I'd like to get the total amount of memory assigned to VM's on a host by host basis?

Any help would be appreciated.

Thanks,

Ben