That's going to depend on things like "how many simultaneous builds do you want to have going" and "how demanding are your tests". A 4gb/2ghz machine should be

That's going to depend on things like "how many simultaneous builds do you want to have going" and "how demanding are your tests". A 4gb/2ghz machine should be fine, but in general I'm not a fan of putting anything but production on production machines.