i have troubles to overclock my system.

with default Vcore. i can not go more than 235fsb. in 240fsb it gives blue screen when entering to windows or resets. i run it with Vcore 1.5v at 262fsb but can not go anymore.
my old D830 can go up to 260fsb with default Vcore.

i heard that 945 chipset have overclock problems with presler series. anybody know how i can solve that problem?