When planning to upgrade from one version to the next newer here I generally end up setting up a dual boot to evaluate it along with getting familiar with the differences before replacing the main currently in use.
Let's see dos/3.1, 3.1/95, 95/98, 98/XP jumping over ME!,
to see XP/Vista, and now XP/Vista/7 betas.
I never seem to have time to upgrade over one version since I was always seeing a clean install of one or another. By the time 7 is out you may end up dumping XP to make space for 7 in a dual with Vista there.