We aim for this to be a Windows PC title with a MAC OS-X support as a stretch goal.
We are targeting the following system as our min spec:
2+ghz processor (multi-core is an advantage)
2gb of ram (1gb available for the game as a minimum.)
GPU with at least 512megs and shader model 4.
We have a lot of options that can be enabled/disabled so that we can run on lower end hardware while rewarding players with higher end systems to nicer visuals. We are looking into trying to support shader model 3 as well, but cannot guarantee it.