For desktop applications like MS Word, Spreedsheet apps, and other desktop applications all being 32bit you wouldn't run into any compatibility issues running a 32bit edtition of either XP or Vista with Vista being the latest version of Windows out.
Following the next version now labeled code name Vienna or Windows 7 Microsoft may no longer release any 32bit editions for the versions to follow. That's when everything will eventually start going 64bit.
ADDITIONAL:
One thing further to add here is that when going out to choose any new model laptop/notebook you will likely see Vista Home Premium, Business, Ultimate, and possibly the Basic edition depending on make and model already preinstalled. When ordering direct through Dell they have been offering the choice of OS while models sold retail in stores will see one of the 32bit editions on them there.