Nowadays, it is not only the computer's processor that produces heat! The video board, motherboard, memories and hard disk are also great sources of heat. The thing is: most people give much importance to the processor's ventilation but very little importance to the ventilation of other parts.
A good ventilation is essential to increase the life span not only of the part that gets hot, but of the other parts inside the computer.
We usually say that the most important part of the computer is the hard disk. Think of this: if the processor becomes defective, you just replace it and your computer will work as always. If your hard disk becomes defective and you do not have backup, everything is gone...
Some good cooler manufacturers, such as Cybercooler (http://www.cybercoolerinc.com), have developed specific hard disk heat sinks and fans. This kind of heat sink and fan is particularly recommended to new hard disks, that produce a lot of heat, as well as to high performance hard disks (disks at 7.200 rpm).
The installation of this kind of heat sink and fan is extremely simple and any user can do that easily. You just have to open the case, unscrew the hard disk and screw the heat sink under the hard disk. Following, you just fix the whole thing back to the case. The fan has a connector that should be fixed to the power supply.
Of course this fan will cool the hard disk, however it will increase the volume of hot air inside the case. That is why you need to pay close attention to how the air flow inside de case is. In computers to regular users, the ventilation that comes with the case is enough. This ventilation is based on the fan in the power supply, that draws the hot air from inside the computer and throws it out the case. The openings placed in the front part of the case allow the cool air to get in, creating a perfect air flow.
In high performance computers, that is, with parts that get very hot (high performance processors and last generation 3D video boards), it is interesting to think about increasing that air flow, through the installation of an additional fan in the PC case. That fan should be installed in a proper place inside the case, in its front part, under the hard disk bay. That fan should be installed in the ventilation direction, that is, forcing the cool air to get in from the outside to the inside of the case.