While doing some recent beta testing (shhh), I realized that my lab is NOT 64 bit compatible. :( I will have to do some searching around to find a suitable 64 bit lab that will fit into my budget (both initial and Electricity!).
A quick and dirty way to check if your current ESX setup is 64 bit compatible is to putty in and run ‘cat /procs/cpuinfo'. Look for the LM flag to determine if you have 64 Bit extensions. (Long Mode)