Most modern desktop personal computers are equipped with detachable power cords and switching power supplies. A switching power supply is compatible with both 110-120 volt North American electricity and 220-240 volt electricity used in most of the rest of the world.
Most of the time, there will be a small switch (usually red or orange) on the back of the PC, near the cooling fan, and it's usually labelled "115V" in one position and "230V" in the other position.
In other cases, the power supply might even auto-detect the incoming voltage and switch itself automatically. That's usually harder to determine though, it usually involves taking the outer chassis off of the PC and examining the label on the power supply itself. Look for something to the effect of "Input: 100-240V" on the power supply's label.
In either case, if you plan to take the PC abroad, and it's equipped with a switching power supply, you might just need to replace the cord. Simply make sure that the physical switch is set to the proper voltage setting (if applicable) and attach the an international PC power cord with a plug that matches the type of outlet used in the destination country.
This specific cord is equipped with an Australian AS-3112 plug.