By "supplied with two wires", I presume the existing supply wire is #12-2 or #14-2 with no ground.
If the outlet boxes are metal and solidly grounded, the new outlets will be grounded when they are rigidly mounted to the boxes. A short ground wire from the outlet ground terminal to the metal box can also be used. If the boxes are non-metal or ungrounded, a separate ground wire should be installed from the new outlet ground terminal to the nearest system ground. If the boxes are metal and ungrounded, they should be included in the ground connection.
Your anonynimity makes answers based on codes very difficult. But, assuming you are in the USA, the National Electrical Code permits replacements to be without a ground if you are in an area where no ground contact is likely. It also permits replacement with a GFI (ground fault interrupter) type of receptacle because a shock hazard to ground would be sensed by the receptacle and power turned-off. If you use a GFI, and put it as the first receptacle in a series, then the rest can be with a ground prong that has no ground connection IF you label each one (labels for this are shipped with the GFI's now). It is best if a ground connection is available, or added. You can connect a separate green or bare grounding wire from the box to the nearest available ground, but this connection is best if it is brought back to the power panel.
Your desire to do this right is commendable. Don't get discouraged if it proves to be time consuming. Many of those older receptacles are downright dangerous because the spring tension to make good contact to a plug is so poor that they can overheat and even cause fires. Be very careful to ensure that the power is off before doing any work, and be prepared to reinsulate wires if the old insulation has become brittle or even started cracking away. Also, be very careful to ensure that the "hot" and "neutral" are on the proper terminals of the replacement receptacle.
Outlet Installation
Re: Outlet Installation
