Here is a nice tutorial for those who work with crystal structures.
http://www.youtube.com/watch?v=jt7qlWTBZqUto calculate d-spacing in excel from 2-theta,
type in excel
=A1/(2*SIN(RADIANS(A2/2)))
where in A1, there should be x-ray wavelength.
A2, is the 2-theta value.