Hi i have a Acer Aspire M5640 with Pentium dual core and a nForce 630i chipset i was wondering if it could be upgraded to a core 2 quad or a core 2 duo

It depends... some have gained BIOS updates. Check with Acer. I'll tell you, in theory it will work as long as it is 1066mhz or even 1333Mhz. You could try cross-flashing the BIOS but that is a huge risk!

is the pentium a new pentium? that is the same as the core 2 - pentium 2200.

if you have a 530 or 820 probably not
what chipset do you have? you need that info first

i am going to post this again:

While THG has articles on updating oem pc's its a waste of time and money.

if you have a low end dell, hp acer or what ever do not waste your time. Its an endless cycle of upgades and in most cases you be better of ebaying the computer and starting over.

typcially one wants to upgrade the gpu but the psu is too small, next you want to oc the cpu but the bios sucks. Bottom line is once you starting replacing psu's, mobos and gpus or cpus you be better off with a used good computer to start with.

do not stuck in an upgrade cycle from hell - u been warned!