Seems Like Alan Wake is Vista only and they are not sure on dx10 support yet
Woot Quad Core Comes in handy for this game at least
4) PCGH: Does the engine profit from CPUs with four or even eight core? If yes what is the expected performance gain resulting from four or more cores?
Markus Maki, Remedy: Alan Wake currently runs faster and smoother on quad core systems than on dual core. Depending on the gameplay situation, the performance gain can be about 30%. We haven't looked at leveraging 8 cores to the max yet.
8) PCGH: Will Alan Wake as announced be a Vista-Only-Title? Will there be any chance for players with Win XP to play the game?
Markus Maki, Remedy: It is best to consider Alan Wake to be a Vista exclusive game.
http://www.pcgameshardware.de/?article_id=629024