Obviously you generally don't want to buy a 2010 title just to turn all the effects down to low; but having said that, for people who are wondering, SC2 is not actually a demanding title, as these things go. Which is to say, if you are prepared to turn everything down, you can actually get "good enough" gameplay, on a pretty minimal machine. You wouldn't want to be training for tournament play
, but if a weaker machine is all you have right now and you are wondering whether to buy SC2 or not, I'd say buy.
My 2c.
My 2c.