I've always been a big fan of windows operating systems... i don't like vista, but that is just me and my tastes. One thing that I would never do, no matter the os... is upgrade it on a personal box. Seriously... just dump the files you need somewhere else and then INSTALL FRESH. If it's a cost concern, go ahead... pay the cheaper price to upgrade... then... when you actually need the full install disk it's going to be found in the same pair of pants you put that time after the party with all of the alcohol and the whores.... never to be found again...
seriously, please dont consider upgrading. no point... doesn't even save time in the long run.