Question

At what approximate temperature and pressure can all three phases of water exist simultaneously?

0oC, 760 mm Hg
0.01oC, 4.58 mm Hg<--Im pretty sure this is correct?
80oC, 380 mm Hg
100oC, 760 mm Hg

Answer 1

that is called the triple point, I think you are correct
http://en.wikipedia.org/wiki/Triple_point#Triple_points_of_water

Answer 2

you need a phase diagram for water, as @cuanchi shows you. Check the graph and you'll see