These files are in PostScript format. It is recommended that you read through the MPI Overview first. It is quite lengthy, so you might not want to print it out. Just use ghostview. Not all pages will be of interest to you.
MPI Overview (Postscript, 961K, 154 pages)
Compiling/Running Guide (Postscript, 519K, 39 pages)
MPI Quick Reference Sheet (Postscript, 72K, 15 pages)
Other documentation
(Argonne National Laboratory)