rover, just because you only have a two prong outlet in wall doesn't mean your house wireing isent grounded.
what you can do is, get a three prong outlet to replace your two prong outlet, remove the two prong outlet from the wall.
what you should have is a hot wire and a neutral wire attached to the plug.
if the house is old it will have bx wire, with a metal jacket around the conducters, that is in a sense your ground, the outer metal caseing wich should be attached the the caseing of the box in your wall wich supports the receptical.
on the new receptical you should have a green screw, what you need to do is attach a wire to the green screw and the other end to the caseing of the box wich will give your receptical a earth groung.
if in dought, get a pro to do it for you . you will be charged anywere from $55.00 dollars an hour to 80.00 dollars an depending on the company.
it should only take a half hour to ground the receptical, unless the circut your working on has no means of grounding, thats another story.