AmitC (San Diego Supercomputer Center) and myself have written and just posted a set of tools to read and write Maya Particle Data Cache (PDC) files. Take a look at:
http://visservices.sdsc.edu/software/maya/utils/pdc.php
The read_PDC program will take any Maya .pdc and display its contents in plain text format. Source code in C provided.
The write_PDC program allows you to write any text or numeric data (particle coordinates, attributes such as color, radius, opacity, etc.) to properly-formatted .pdc files that Maya can use directly. Source code in C++ is provided. Currently, the write_PDC program just generates particles on a grid with different colors and radii, but all of the write functions are there, so it should be very straightforward for anyone who knows C++ to modify the program to output their own data. We plan to update this with another example that will convert a text list of particle coordinates without programming, but we wanted to post just the binary-file-writing code now so programmers could use it right away.
We're still working on this, so any feedback, suggestions, or modifications would be welcome!
Thanks!
Peter