How did the Egyptians build the pyramids (Giza in particular)?

Before you say anything dumb, I don't think extraterrestrials did it. But I was watching a segment on the History channel and it talked about how most of these blocks weighed around 2 tons, and there were 2.3 million stone blocks used. TODAY, architectural designers say a feat like this would nearly be impossible today, even with the MACHINES we had today. How did the Egyptians, not having any advanced tools (we suppose), build these mega-monuments. The architectural designs are nearly perfect so that you could barely slip a piece of paper inside one of the crevices of the Giza pyramids. I understand that the pyramids are "supposed" to be used as a burial site for the Pharaoh(s) and all his/her treasures. But wouldn't something that big be an easy target for grave robbers? What if the pyramids had another purpose; the Giza pyramids do line up with stars in orion's belt and they are geographically located at the centre of the planet (if flattened out). What if they had some advance tool given to them by advance beings from another planet. I GIVE the Egyptians credit for building these pyramids, but what was the all determining catalyst? As you look all over the world you see similar structures to the pyramids, such as in South America and Mexico, but the Egyptians and Inca/Aztec/Mayans/etc didn't mingle or share ideas, or did they? How can pyramidal structures be so common all over the world?