I also o'clock this baby to 400*9 =3600..
But i face the HDD prob too previously...The HDD timeout and cannot shut down.
Yesterday i foud out that i didn't move the HDD jumper...

...Now malas to try already.... After HDD timeout, will create a lot of error event in OS...Tired to do that format and reinstall things again...
So in sumarry, this E6600 can o'clock well... It can do >400FSB with no prob...
I think the most importance things for o'clock is:
Press Ctrl +F1 in MAIN MENU and try this settings..
CPU Clock Ratio : 9X
CPU Host clock control : Enabled
CPU Host Freq : 400
PCI Express Feq :100
CIA2 disabled
System memory multiplier: 2.0
Memory freq: 800
DRAM timing :Manual
SYS volt control : manual
DIM over volt control:+0.2V
PCI-E "" "" "" :Normal
FSB "" "" "" :Normal
MCH "" "" "" :+0.2V
CPU volt control: Normal
Normal cpu Vcore: 1.4V
Ram timing depend on your ram. Some said the BIOS got some prob with D9 RAM...(Cannot o'clock >1000)
Above setting will make your E6600 run in 400FSB