Great question. I'd think there's only one way to find out. LoL. I know you'd like a more definite answer or some well-thought-out formula, but honestly, I think you'll jsut have to see how much the running impacts your overall recovery and legs.
It depends on how far you run, how hard you run, how many hills you run, whether you're eating properly (taking into account your extra activity), how much volume your doing in your weight training, etc.
IMO, healthy people ought to be able to run 2 moderately-paced miles and still lift w/out much negative effect. If you can't do that, IMO, you need to get your cardiovascular system back into shape. LoL Two miles at a moderate pace shouldn't kill you.