ESXi vSphere (v4) performance monitor question

[withanh]

My hardware is dual 3.2GHz Xeon (Hyperthreaded) and 8GB Ram.

I have three VM's running

VM 1 Windows 2003 server/DC
CPU count = 2
RAM = 2GB
CPU avg MHz = 169
CPU avg % = 2.6

VM 2 Debian Lenny (v5) LAMP server
CPU count = 2
RAM = 1GB
CPU avg MHz = 39
CPU avg % = .624

VM3 Windows XP
CPU count = 2
RAM = 2GB
CPU avg MHz = 152
CPU avg % = 2.3

But the machine says
CPU avg MHz = 3241
CPU avg % = 50

How can I have three machines basically idling, when the total MHz is 50%? Can someone please explain to me how the performance monitoring actually works and what the numbers really mean?

Thanks!