I have continued to develop a computer program for calculating non-collinear phasematching parameters and other useful quantities related to downconversion. I developed this program while working at NIST, and still periodically receive incquiries, so I've published the program as it stands (as of 2008). To install the program
The computational portion of the code is written in Fortran. The graphical front end is a small Labview application that calls the Fortran library and displays the plots. The Fortran source code is also included in the zip file. I continue to develop this code, so if you find bugs let me know.