The requriements for Starcraft 2 have not been released yet. The game hasn't even gone to Beta. However, Blizzard is known for making their games compatible with a wide range of hardware ranging from low to high end.
I suspect, if you build a new machine now, that you will be able to run Starcraft 2 without a problem.
honestly, from the videos i've seen the graphics don't look that good...still nice though. I'm with allanag, they don't want to alienate customers (ahem crytek) by ramping up system requirements too much.
well most people in all the 50 billion blogs ive been reading have been thinking that it probably wont be coming out this year but maybe if were lucky mid 2010, also with our current economy dont expect it to come out anytime soon. the system requirements will be basic, blizzard always does this to get good sales and mass people on bnet. i also worry because i have an old 2003 or so gateway laptop with a pentium 2 and an old stock graphics card from intel(the crappiest company ever), 225 mb RAM, and only 14 GB OF MEMORY!!! so lets hope its good even though im hoping its just a good game and not rushed.