My Notebook currently has an Arrandale CPU (i5 520m) and a PM55 Chipset.
The question is, because I know I could pick every Arrandale CPU, if it would be possible to use an newer Sandy Bridge CPU or even a Ivy Bridge CPU.
I came to the point that this Chipset would/could be the only issue (cause its soldet to the Mainboard).
Depending on how the laptop manufacturer configured the computer then the processors that will work with the laptop. I recommend contacting the laptop manufacturer so; they can give you the list of compatible processors.