Xeon and Core 2 Duo belong to the different processor classifications of Intel. The Xeon is known to be very versatile because it will have the ability to work in an environment wherein there are different processors that are involved. If in case you are not aware of what this means, this simply means that you can sometimes have two Xeon processors in one motherboard.
This is something that you cannot expect from the Core 2 Duo. When you have the Core 2 Duo processor, it is the only processor that you would be placed on the motherboard. Take note that this is recommended more for those who have businesses and workstations because this is known to work better that way there.