Yes its possible to simply install new motherboard and not have to reinstall windows, but for a begginer its something I would recommend.
He will need to know exactly what he has atm and exactly what the new motherboard has.
ptto - If you do want to risk it, I recommend you post here what your current motherboard make and model is, and as Ghislain said, what chipset it has, as well as a link to the new motherboard you wish to purchase.
This way we can tell you if itl be the same chipset and you can try simply installing new motherboard without reinstalling windows, at this point, making sure you backup first just in case.