I've got x-ray powder diffraction (XRPD) data on bendamustine HCl from a patent and I want to know how to construct a 3D model using this data with software.
It is possible to reconstruct molecular structure from powder X-ray data. It is called the Rietveld method: http://home.wxs.nl/~rietv025/ http://www.aps.anl.gov/Xray_Science_Division/Powder_Diffraction_Crystallography/
However, it requires high quality, high resolution data (meaning generally synchrothrone powder data), and it is an involved process which requires some experience. Most probably you don't have that quality data at hand, you don't have time to learn and figure out yourself try-and-error and most probably you don't need the result either. If you need some general insight how the molecule look like, I would join to Abel Friedman and suggest using simple calculation techniques. Molecular mechanics and other low-cost methods can give very good structure with minimal effort.
What do you hope to achieve? It is possible to obtain accurate interatomic distances from powder data (here is an example, the structures of several alkali metal cyclopentadienides), but the method is non-routine, and the data-parameter ratio is low, which means that you cannot refine many parameters and must put much information in through appropiate restraints. You still need accurate peak shape data.
If you just want the general shape of the molecule to illustrate Wikipedia, you are better off with obgen from the OpenBabel project. It usually gives good results.