The HSF (Heat Sink/Fan) that comes with many video cards, as well as a lot of CPU's, are only sufficient to cool the component at the stock speed, and occasionally you even see some that don't work properly at default speeds! When components become overclocked, they produce more heat and the default coolers wave small white flags in the air surrendering. The solution to this rather annoying problem is to buy better cooling equipment.
In the CPU market, there are hundreds of coolers to choose from with choices ranging from fan size and speed to the material the heat sink is made from. Unfortunately, the video card cooling market is a lot smaller, and basically consists of one company. That company is Thermaltake, who makes the Blue Orb and Crystal Orb. The other option people have is water cooling, but that is reasonably hard to implement and is impractical in most places.
The only real options here are the Thermaltake Blue Orb and Crystal Orb (you can go water cooling here, but i doubt you will want to). The two Thermaltake products look like this:
This is the Crystal Orb. Not exactly crystal, but at least it's silver.
This is the Blue Orb. If you want to know more about these products, then go to the manufacturer's webpage.
The cooler to buy is, without question, the Crystal Orb. The Crystal Orb is made of copper, instead of aluminum as is used in the Blue Orb. Copper is regarded as a better material to make heatsinks from, as it conducts heat far better than aluminum does. However, the Blue Orb still does its required job very well. One thing to remember is that both these coolers are 5500RPM models so they don't sound like your PC is ready to take off.
The installation of a new cooler is a reasonable easy affair, so don't worry. If you want to fit one, try these steps:
(1) - Take the old cooler off. If it is joined by push pins, squeeze the end bit on the back side of the card and then push the pin up and the cooler should come loose. The material between the cooler and core can play an important role here. If the material is thermal paste, like Arctic Silver, then you will likely have push pins, and the cooler will come off with the step above. However, if your cooler is connected through thermal tape, you're in a spot of bother. These can be really hard to get off. The most common way to get this stuff off is to use a knife or similar object and pry the cooler from the tape. I have also heard that putting it in the freezer and similarly crazy techniques that can work to get it off. Be warned though, using a knife to pry the cooler of can obviously damage your card. Thermal epoxy is another method of keeping coolers on cards and this one sure doesn't come off easily. You may as well get a different card if yours is connected using this method. Why? You will most likely destroy the card in the process of taking it off.
(2) - Once you have the old cooler off, apply a thin layer of thermal paste, like Arctic Silver (recommended), over the core. The thermal paste is intended to fill tiny gaps between the core and the base of the cooler so you don't need to spread this stuff like your making a sandwich. If you're not using thermal paste, go to 4.
(3) - When the thermal paste has been applied, place the cooler onto the core, and push the pins through the holes. These should not come back out, but if they do, check for broken pins and that you are doing it the right way. Go to 5.
(4) - If you're connecting with thermal tape, simply stick this onto the base of the cooler, and stick it onto the core.
(5) - Once the cooler is attached, you will need to join the fan power cord to a fan header. Join it to any header, but if you want to monitor the fan speed, make sure you join it to a header that supports this. Another option is buying a 3-4 Pin adapter which can lessen the stress on the motherboard, but a 5500RPM fan shouldn't cause much of a problem.