Relativity says that there is no special position in the universe. Or equivalently, every position is the same as every other as far as the laws of physics are concerned - with the caveat that the speed of light in vacuum is constant.

Geocentrists take advantage of this equivalence by saying that they believe the Earth is special and demand proof that they're wrong.

One of the easiest demonstrations to understand for the Earth moving is the [link|http://www.music.sc.edu/fs/bain/atmi02/foucault/pendulum.htm|Foucault Pendulum]. If you believe that F=ma and the rest of Newton's Laws, then the simplest explanation for the motion is that the Earth moves. The motion can be described in a geocentric Earth coordinate system, but it's much more complicated to do so and requires additional forces (like a strange new form of gravity that doesn't show up in other sensitive measurments). Even some creationists think [link|http://www.answersingenesis.org/tj/v15/i2/geocentrism_review.asp|geocentrism is bunk].

HTH.

Cheers,
Scott.