Ah... the newcastle can do pretty good, but watch the heat since it is 130nm core wafer build. The silicon can only handle a max of 67-69 degress celcius! I recommend stopping on AMDs at 58celcius, dont go higher, it shortens the processor lifetime.
Now, since the multiplyer is locked, you need to use the FSB. So this OCing will really stress the MOBO and northbridge controller more then the CPU. Make sure the voltages are stable and run prime95 or HOTCPUTESTER 4 after each OCing stage. Here is how I would do that.
Stage1: FSB=215MHz HTx=5X
Stage2: FSB=225MHz HTx=4x
Stage3: FSB=240MHz HTx=4x
Stage4: FSB=260MHz HTx=4X VOLTAGE= 1.575V
Now, you can go higher, but watch the heat. I wouldn't push it over 3.0GHz if I were you, especially with Air Cooling... Liquid or phase change, you could go 3.5GHz or so, but no more then that stability wise.