You can't ground the adaptors. You'll need to see if you can change the 2 prong receptacles to 3 prong receptacles. To do this you will need a voltage tester. Take a reading from the hot (black) wire to the metal box. If you get a reading of 120 volts or a light using a neon bulb tester, then that indicates the box is grounded.
If the box is grounded then you can install a self-grounding 3 prong receptacle. If the box is not grounded then you can install a GFCI receptacle to replace the 2 prong. This will allow you to plug in a 3 prong plug, but you will still not have a ground. Those are your only choices.
Here's a link that'll detail all of this for you.
http://www.codecheck.com/250_50_commentary.html