My guess at recommended:

2.6Ghz Single Core
2gig ram (xp)/3-4 gig ram (vista)
512mb Graphics Card (a decent one too, high 8000 or 9000 Nvidea series, I dont know how they compare to other brands like ATI)
etc etc

CA have stated they wish ETW to be playable for a large range of computers, so you can always hope.