ESXI is its own operating system that you install if you want to cluster it you'll need to purchase vsphere. You'll need windows 2008 ENTERPRISE w/ hyper V to create a cluster and use it for virtualization.
All of which are expensive. Clustering isn't cheap.
I have two computers.
Intel i7 930
24GB DDR3 1600 Ram
2xIntel Xeon E5620
24GB DDR3 1066 RAM
I want to link those together and then create few virtual systems. Basically just like vmware esxi but on two systems linked together as one