A lot of users often asked if it was ever possible to run two systems with a single power supply unit. While some users reported success, it wasn't something that we would encourage since most of today's processors would be too power hungry. It may still be possible to power up two of the latest Intel Pentium D or Athlon 64 X2 systems but you may need to get a pretty powerful power supply to get it working.
Fortunately for today, both AMD and Intel have introduced new processors that are less power hungry. Intel's upcoming Conroe processors (known as Intel Core 2 Duo) would draw only about 65W while AMD's low power Athlon X2 processors that were recently announced would draw 65W for the Energy Efficient model and 35W for the Energy Efficient Small Form Factor model. These processors are powerful dual core CPUs which gives you a lot of mileage in terms of compute performance and would make great machines for all sorts of purpose, be it gaming, video rendering or even a workstation.
In order to get two systems running from a single power supply unit, one would need to construct a customized 20-pin ATX power cable with a single female connector on one end and two male connectors on the other. This would multiply the regular 20-pin power cable in your power supply unit to support two motherboards. We went to a regular electronic hardware store and purchased a couple of male and female connectors along with the pins that go along with these connectors. Constructing the cable is just a simple and long-winded process of crimping the cables together.
To really quicken the process, we took two old 'about-to-discard' power supplies and cut out the ATX power cable. This will give us the ready made end of the two male connectors along with corresponding color coded wires. The next step would be to match the cables pin for pin and have them crimped with the pins. You just have to make sure that all the wires are crimped correctly (e.g. pin 1 should go to pin 1) and you'll have a Y-shaped ATX power cable as shown in the picture below.