Increase the FSB by small increments to begin with, and I'd recommend only overclocking it to the maximum that the default voltage is capable of. Monitor your temperatures and system stability for a few days, and if all seems fine, increase the voltage and slowly increase the FSB once again.
Once you get over 55-60 degrees under load, I would recommend stopping until you have better cooling availible. Also remember to make sure you aren't overclocking the memory or video card at the same time, unless of course you feel they can handle the heat.
Intel C2D E6320 / AMD Athlon X2 3800+
Gigabyte 965P DS3 / DFI nF4 Ultra-D
2GB OCZ Gold PC2-6400 / 2GB OCZ Gold PC4000
eVGA 8800GTS 320MB / eVGA 6800GS 256MB
150GB Raptor / 74GB Raptor
2x500GB / 320GB
OCZ GameXStreme 850w / OCZ StealthXStream 600w