If you have any AMD drivers for the CPU you could uninstall those first. But really you shouldn't need to do anything. It's not like you are swapping your motherboard out.
it depends on the motherboard you have. like i just swapped my nforce4 for a nforce650i Sli and i didnt need to format,but when i switched out my VIA board to the nforce4 then it wouldnt let me do it. so similar chipset means it will work with an updated chipset in the same series.
The only time when I did have to reformat was when I replaced my graphics card, because I couldn't be bothered to swap them out again and unistall previous drivers