Swapping out logic board components?

Hi. I have a 1st generation MB Pro (2ghz Core Duo processor, radeon x1600 card), from the very first that came out. I've upgraded about as much as I can on this computer without swapping out the logic board- RAM (up to the 2GB max it allows) and hard drive. I even swapped out a fan since this one was one of the models with that mysterious buzzing sound.

However, my computer sometimes shuts down at random times, and I think it's either because of the temperature sensor, or the graphics card or processor go nuts at some point and just turn the whole thing off. I suspect it is because of this, because it usually acts up during graphics-heavy operations (Photoshop, watching too many videos, trying to rip a DVD, etc).

My question is, is there a way I can swap the logic board out for a better one (from a later MB Pro model), or am I better off buying a new computer if I want to upgrade?