It is very difficult to transfer an existing Windows installation from one set of hardware to another. Theoretically it is possible, but I've never done it or seen it done. Usually the result is a blue-screen-of-death during boot. Don't bother.
As to transferring your Windows license, it won't work either. Major vendors like E-machines (owned by Acer I believe), have volume licensing agreements and their OEM Windows license will not validate on your new motherboard. Those licenses are sold cheaper because they "die" with the original motherboard. You'll have to buy a new Windows license.