thanks for getting into green data center usage. it is good to know that you are trying to save electricity and cooling costs which will also help the environment. using virtualized servers to save on rack space and hardware usage is a great start. it will drastically cut down on your expenses as far as electricity usage, cooling needs and up front hardware costs. here is a great article that I have found on the issue: Build a Green Datacenter.
this should help you in starting to get your project underway.