Cool your system with water and overclock even further
Pump - This pumps the water around your system. Things to look for are the flow, pressure, heat issues, and noise. All will be rated and the pressure and flow are vital depending on the amount of blocks and distance you need the water to pump through your case.
Radiator - Just like a car radiator this removes the heat from the water by separating the water into smaller parts where air can cool the pipes and as a result the water.
Fans and Shrouds - Shrouds are used to mount fans to the radiator, with fans being set an inch or two away from the radiator set to draw air away from the radiator.
Reservoir - This is the storage area for excess water; these are not essential but are normally preferred as with one there is less upkeep. Again like a car this should be a sealed system with no air.
Fluid - You can't just use any fluid or water. You should use distilled water or de-ionized water. The reason is these are less conductive than drinking/boiled water, so if water was spilled or leaked the chances of saving the rest of your computer are far higher with distilled water or de-ionized water.
Clamps - Not essential but they help keep the various tubes in place.
Tubing - Connect the different blocks and parts together and carries the fluid.
As you can tell from this short summary you will need to source a large number of parts to put together a watercooled system for your PC. And the size of the kits can vary vastly in price from £70+ for a system for an average tower system.