If you only have two wires entering the outlet box then you do not have an equipment ground. The fact that your house is 50 years old leads me to believe that there is no equipment ground. If you have ground wires coming into the the panel it may be that the panel was replaced and some new cable may have been run to parts of the house but probably not down to each receptacle. Grounds are very important to have, they do more than offer protection from shock. Read the post about self grounding outlets from yesterday.
You should not have replaced the two holed receptacles with three holed. This is a violation of code. You should have used gfci receptacles if you cannot provide a good path to ground.
As far as the utility company's ground is concerned, No they do not even supply a ground wire to your house. They provide a neutral wire which is center tapped from the transformer. When this is bonded in your fuse box and also bonded to the grounding electrode then you establish a ground.
You can ground those outlets to your existing grounding conductor by adding an extra wire, but it must be continuous all the way back to within 5 feet of where the service enters the house, Or you can take it back to the fuse box and ground it to the neutral bar. Let me know if you need more help.
[This message has been edited by ElectrcBil (edited October 26, 2000).]