I remember the first time I knew that the earth was round, was thought in Geography class back then, the first question that ran through my mind was ;where would i end up if I started digging straight down?. I even remember asking my Geography teacher this question, he simply told me it is not possible , Yes I knew it was not possible scientifically but just for the fun of it,I wanted to know, I was just curious to know.

Have you ever wondered where you would end up if you started digging straight down?
Another interesting question, let’s assume, you had a drill capable of plowing below where you are standing right now and grinding its way straight through the middle of the planet to the other side and you jumped inside this hole? Would you come out of at the other side? Remember gravity will always pull you toward the center of the Earth .What do you think would happen?

No technology exists, for now, capable of drilling all the way through the earth. High temperatures and other conditions would sabotage drilling apparatus with increasing depth.

http://en.wikipedia.org/wiki/Kola_Superdeep_Borehole