Assuming you just planned to make a browsing pc, one that can decode the latest movie clips (nothing big). And post on forums and just browse in general, what would your cheapest setup be? I'm considering building one just for backup purposes, since my main pc isn't really stable now, it'd be nice to be able to come to places and ask without spending a few hundred on another real pc. I'm talking bare minimum here, just enough to read and browse websites and watch mpgs, avis, and the like.
