3. You need an aftermarket cooler like a 212 Evo for good results. (inexpensive yet effective)
Like anything, OCing does involve some risks - if done correctly, the risks are small. Your cpu with an EVO cooler should get close to 4.0 GHz.
p.s. - what is your psu - do you have ample headroom for OCing?
Playing around with the voltages can potentially damage your cpu and can reduce its lifespan. You can change these only if you know what you are doing.
If you have an unlocked cpu, the safest way to overclock is to slowly increase the cpu multiplier and run stress tests each time you increase to test for stability. You can get a few hundred mhz without touching voltages.
If your cpu is locked, you can increase the fsb frequency slowly (5mhz or so at a time). Make sure your ram is not linked to the fsb speed or you could accidently overclock your ram.
The case fans have little to do with cpu overclockability. You need a good aftermarket heatsink to really get a good overclock.
@flexxar: There's no Black Edition (unlocked) for the 945, so it's locked.
thegambleruk, for reliable OCing help you should at least give us more info on the motherboard, memory and power supply that you'd be using. Overclocking the processor is somewhat of a comprehensive issue - in other words, the kind of motherboard you have is a major variable, so is the memory. Not to mention, in some instances it might not even be worth the effort. Mind listing those to us?