i just found this:
There have been situations in which a chip manufacturer will deliberately underrate a chip in response to market pressure. This results in an inexpensive component that (with a little extra voltage) is easily overclocked to match the speed of a more expensive component. One example is the AMD Athlon 64 X2 4400+ (codename Toledo) processor, which was easily made as fast as the AMD Athlon 64 X2 4800+, simply by increasing the voltage and clock speeds. Manufacturers will often sell these processors at 50% extra. Users can often easily overclock a component to above the highest settings a manufacturer will sell a component for.
Recently computer experts experimented with a Pentium 4 3.4 GHz HT processor, cooling it using liquid nitrogen, and blowing cold air at high speeds past it. They managed to achieve over 3 GHz above the original frequency, which is a considerable amount. Few users would tolerate regularly topping off their computer with liquid nitrogen, the noise alone of such a system making it impractical. These tests are interesting, however, as an illustration of what is possible when great amounts of heat can be removed from a system and are an indication of what could be achieved with better (but not as drastic) cooling.
So dont be scared of overclocking it some.