Some people seem to think that you do. I have tried using sysprep(located on the XP CD) to install a new Mobo. It works and save a lot of headache. After my swap From Asus to DFI I am glad I did the re-install/ format and partitioning. OSes in general seem to be better but that might just be the board.
I think you'd be ok. The chipsets are similar enough that you should be able to just do a replacement without too much effort (maybe a Windows activation). They are different drivers (at least they used to be), so I'd just make sure I have the newer ones on hand for the swap.