How many sticks of RAM?
Set your vcore to 1.3v then start upping your FSB in 10-20MHz increments and seeing if they boot windows fine, or go straight to 333MHz FSB if you're impatient and then run Prime95 small ffts (updated version that runs on 4 cores) for a good few hours keeping an eye on temperatures using CoreTemp.
If Prime95 fails and the temps are <75 degrees C, increment your vCore by about 0.05 and try again.