Format NOT required.
Prior to your final shutdown do the following -
Change the IDE driver to a "Standard dual IDE driver".
This is done by using the device manager.
-Click the + next to "IDE ATA/ATAPI controllers"
-Under that is primary, secondary and the parent entry (Via, Intel etc)
-Right click the parent entry and select "Properties".
-Click the "Drivers" tab, then choose "Update Drivers"
-Click "Next" then the "Display a list (etc)".
-Select "Standard Dual channel PCI IDE Controller" and follow through to the end
Failure to do the above will usually result in a BSOD first boot with new mobo.
If use use SATA the method is essentially the same.
You have to manually remove the old SATA driver and ADD the new SATA drivers prior to your last shutdown using the "Control Panels" "Add/remove hardware" application.
Uninstall the old video card drivers before replacing the mobo using the Add/Remove Hardware applet again.
Uninstall any onboard devices drivers i.e. network, sound etc.
Replace your motherboard/video card and reboot.
Install the correct chipset drivers for your new motherboard (usually inlcudes the correct IDE driver, if not install them also.)
Install new video card drivers.
Install any other drivers for new onbaord stuff.