You will need to mask the NX/XD bit in the settings of the VM -
You can also look into your BIOS (of the Dell Servers) if there's an option to activate the NX Flag.
There are 10 types of people. Those who understand binary and the rest. And those who understand gray-code.
If you are using ESX 3.5 Update 2, you may want to look at EVC (Enhanced vMotion) option.