You can start by reading this thread grounding outlets
As for using a GFI on a 2 wire, it will have to be placard as a "Un-Grounded" outlet, otherwise it will be thought of as a grounded outlet. As for updating from 2 wire, how hard would it be on a scale of 1-5.
For instance, my house is about a 3, due to I have 2 wires in the walls going to light switches, that would mean either pulling wire up a common wall to go through the attic and back down, or leave it at where I have gotten to so far, and that is switching out all of the outlets, and leaving the lights. The wire for me was all 2 wire Greenfield, and originally only 4 circuits to control the whole house.