What >>4 said.

And you don't have to upgrade everything either. As long as you have some basics covered (like enough RAM and hard drive space...) chances are that the computer you're using right now can do pretty much everything you want. Except games.

I've been using a 500MHz P-III as my main computer for the last four years, and it does everything I want, like downloading/watching anime and porn ... I mean movies. Web / email / schoolwork / programming obviously is no problem either.