Is overclocking healthy for my computer?

Get a good cooling system.

…and if I have a good cooling system I should have no problems

If its done properly, then yes, it is pretty safe. What you have to remember is that overclocking basically increases the amount of power you are putting in to the chip this means that the chip will get hotter so cooling is very important. This doesn’t have to be anything fancy but you need to make sure all the fans are working and the heat sink is properly attached to the CPU (this is particularly important if you built the system your self). Also remember that air cooled cases are designed to function best with the side on despite what a lot of people may tell you. If you take the side off the fans can’t move air over the heat sinks as efficiently.
If you push the chip too far then the stability of the system may begin to fail, and you may also shorten the life span of the components. Overclocking also usually invalidates the warranty.

Now the real question is “Is it worth overclocking my system?” For everyday computing stuff (internet, word processing etc.) it won’t make any difference at all. Even in games increases in performance of less than 10% are almost undetectable. You’d probably see more improvement just by increasing the RAM (and a faster graphics card but thats expensive). The only place you will really see the difference of a small overclock is in a benchmark

All processors are by default down-clocked.. so to say. Look on the www for overclocking your specific processor, chances are you can find how-to, the point where it runs stable and the cooling that goes with it.

Later 45nm processors almost don’t overheat and can be clocked a lot further then their factory settings. But truth is.. you will find no or hardly any gain in speed. And the frequency don’t mean shit these days.

Core2Duo’s should still run almost every system pretty snappy and 2GB of memory is plenty. If you feel the system is slowing down, look for a faster harddrive or write your current one with zero’s and do a fresh install to get that ‘the-day-you-got-it’-feeling. Overclocking, while pretty safe, should only be done with disposable cpu’s.

The main issue with overclocking is going to be that your processor will run hotter.
If you are going to overclock, first thing you should do if you haven’t already is get a premium cooling unit.

What they said (about cooling), and consider a beefier power supply. Make sure your memory can handle the clock speed as well.

But…

Most people overclock for gaming performance. Before you tinker with your CPU clock, get the fastest graphics card available for your system, and did I mention upgrading the power supply? Think about a SCSI HDD, or at least a 10,000 RPM SATA drive, and load as much memory as your MoBo will support. Overclocking your CPU will have next to 0 noticeable effect when running ordinary Windows applications.