You really can't just drop in a new motherboard and and have it boot right up because of differences in hardware, addresses, IRQs, drivers, etc. If the new motherboard has the same exact chipset and options, then it should be a slam dunk and your system should fire right up first time. But, more than likely there will be differences and the OS is going to pitch a fit and not boot. If you have XP there is a tutorial that shows the steps needed to prepare the OS before the transfer.
Is there a reason for swapping the motherboards?
Swapping your board without so much as a reinstall