Totally depends on how old your old motherboard was and if it was INTEL and now is AMD and stuff like that.
If its lets say a (INTEL) Gigabyte GA EP35mainboard and the new one is just a (INTEL) Gigabyte GA EP45 you should be able to boot into windows to remove all the drivers and then install the ones from your new mainboard dvd/ download them.
But there is no guarantee that when you made all this that the computer wont be slowed down to some extent because you can never remove all the drivers from your previous installed hardware. You would need special software to do this or to migrate your Windows as a CLEAN windows without drivers into a new partition.
I did this a few times and the chances that it actually works are like 50/50 and then there is also a 50% chance that the Windows is slow because of driver conflicts.
So try to backup your HDD and then try to use it with the new motherboard. If its not working then install Windows a second time (use another partition!***)
(***If you have Windows Vista 7 or 8 you can take some GBs away from your Windows partition and create a new partition while Windows is running !!!! this has to be done before you remove your old mainboard and install the new one because so you have guaranteed access to Windows it gets more complicated when you have no Windows!!!)
Install Windows into the new partition. Then migrate the files from your old Windows installation into the new one. (if you cant boot into the old one you will still be able to access all the folders from within your new installation)
And you can also use software that moves all your important files and program/game installations/registries etc into the new Windows
I hope this makes some sence I am tired and a little bit drunk my nephew was born yesterday so we were partying a bit :)
