It is extremely unlikely that you will damage your computer by over clocking unless you:
a: Pull more power than your PSU can provide; and your PSU does not have the necessary protection circuitry
b isable the thermal shutdown in the bios
c:Up your voltages to a ridiculous number.
Your CPU may under clock itself to save power. I think Intel calls this Speed-step. Try testing it under load, or disable this in the BIOS while testing. This should give you a speed of 3.2Ghz, also, download cpu-z and use those readings.
For a first over clock, I would not change any voltages, just use whatever sticky I am sure someone will reference you to at stock voltage. That should give you considerable improvement.
The cooler you keep your CPU, the more you can overclock it, so you should replace your stock cooling solution if you havn't already.
Post your PSU and your cooling solution (stock fan, heatsink or whatever it is) and people should be able to give you a general target, though it really is luck of the draw with what chip you got.
intel i7 960 very fast, strong by default ! if u want set Clockspeed & RAM until maximal under 70*C don't over,
over 70* full load when tested.
see other Temp for healthy :
CPU 70 C max
Mobo : 80~128C max
HDD :50C max