I had this same problem about a year ago. I was getting the same error messages you are. I came here a posted the problem and a lot of very knowledgably and extremely helpful people gave me a lot of great advice.
Unfortunately, none of it worked. I was first told to change memory, then video card, and then drivers and on and on.
It ended up being an overheaing problem. I had finally given up and took into a shop, and was very embarrassed when the tech said the heatsink was clogged with dust. He also said the fan was not turning at a high enough RPM. He cleaned the heatsink and replaced the fan and it was fixed.
So, before you trash your system, or start buying parts, checks to make sure you're not overheating. It may be that you have a different problem, but check that first if you haven't already.