Make sure your CPU clock speed (this is called HTT with the Athlon64, FSB no longer exists) is set to 200MHz in the BIOS. We'll overclock with ClockGen, remember ?

Test stability at stock speed first ! Especially to see what timings your RAM can take at stock speed. If she's not stable at stock speed, don't overclock !

Set your AGP clock to 66MHz in the BIOS (nForce3 only)
Set your Vdimm as high as possible. At least 2.8V is recommended.
Set your LDT multiplier to 2.5X or lower. The LDT multiplies by the HTT (or CPU clock speed) should be less than the max HyperTransport speed your motherboard supports - it's 600MHz for nForce3 and 800MHz for K8T800. If it is too high, your motherboard will reset to Safe Mode and cancel your overclock.