For optimal cooling an aftermarket heatsink/fan combination is best.
You will need to remove the stock chipset heatsink and install a heatsink/fan combination that will fit the existing heatsink's mounting holes.
Chipset Heatsinks/Coolers | Page 1 | Sort By: Product Title A-Z - FrozenCPU.com
Another option is to buy a 40mm fan and mount it so that it blows down and/or across the stock chipset heatsink.
MSI N460GTX Hawk (1GB) Overclocking Results, post #81 shows a 92mm fan that is secured with cable ties to the thick 24-pin power supply cable.