How close is the elliptical to actual running?

It won't do much to improve your two mile, but it will maintain it if you're really pushing it.
I've found the best indoor exercise is shuttle sprints on a turf. Things like versa climber, rower, sled, and bike will help you increase your cardio, but you still need that impact that running gives you or your legs will be toast when you hit the 2 mile test.

Better than nothing but definitely not the same. I usually do treadmill work for speed if I don't have a track but nothing beats running to practice for running. Supplement with bike, weights, and plyo.

Not as good when you're young. Better when you're older and the knees are near shot.