You can try.
If your new motherboard chipset is similar to your old motherboard, there is a fair chance that you will be able to boot into windows using your old "C" drive. If you can, then you need only to install the motherboard drivers that come with your new motherboard cd.
If the motherboards are too different , like going from amd to intel, then you will not usually boot because your old windows does not have the correct drivers.
Here is a procedure that might work, but I have not tried it:
http://www.dowdandassociates.com/blog/content/howto-repair-windows-7-install-after-replacing-motherboard/
If you need to do a clean install, it would be an opportune time to upgrade to a ssd.
To prepare, use windows easy transfer to export your settings.
Disconnect your hard drives so windows does not try to put a hidden recovery partition on them.
After the clean install, you can reattach your hard drives and import your old settings.
Since you have a new clean registry, your programs will need to be reinstalled.
If your windows is OEM, you technically need a new license. But, MS is surprisingly lenient about letting you reactivate with a new motherboard.
They mainly want to be assured that you are not a pirate and that this copy of windows is not used anywhere else.