I think Maziar is off on this one... I'm assuming you mean that you have a laptop with a PM45 chipset. If so... a QX9300 is as high as you can go.
http
/ark.intel.com/chipset.aspx?familyID=35515
There's a list of the processors that chipset supports... just scroll down to "valid processor combinations"
And one word of advice... just because a processor is on that list, doesn't mean your laptop's cooling system is up to the task... each processor's TDP is listed in that chart so plan accordingly.