Sean,
IMO it is not really sufficient on these boards to use a four pin cable on the ATX12v header.
If you look at the PCB tracks on the reverse side of the board, you will see that the four ground pins on the eight pin header are actually connected to two separate ground planes. So if you only use the "right" half of the socket, only one plane is connected and the other is left to float.
There have been a rash of people on the Abit USA forum who have experienced odd inexplicable issues that mysteriously (or not) disappeared when they switched from PSUs with a four pin ATX12v plug to a unit with a proper eight pin cable.
Indeed, using the Corsair HX620's four pin cable as an experiment, my board did some extremely odd things, including the LAN disappearing (a commonly reported fault) and often failing to save its BIOS settings. Plugging the eight pin cable in instead instantly restored reliable operation.
This unscientific test alone indicated that these boards really need all eight pins (or certainly all four grounds) connected.
Anyway, Propolis: You can get four to eight pin adapters that will convert the four pin line on your power supply to an eight pin plug that will mate fully with the header on the motherboard.
As has been said though, you'd be well advised to upgrade your PSU for something from the current generation.