With what OS?
I've went Intel TX to VIA MVP3, to BX, to SIS 630 back to BX, without reformatting with Win98 just to see if it could be done
(done bx to via with win2000 too) and it can!
if you are using win95(heaven forbid!!) you won't have a choice.
however, my recommendation is and always WILL be to reformat Win9x/2xxx whenever you switch something major like a Motherboard regardless of which chipset.