Brad Lucier has installed new math department letterhead macros for amstex and plain tex for the new tex.
You need to have /pkgs/texlive/2005/bin/sparc-solaris/ early in your unix path to use these new macros.
There are sample files showing how to use them at:
/pkgs/texlive/2005/texmf-local/tex/plain/local/
The short version is that after the
\input amstex
\documentstyle{whatever}
lines (if any) say
\input mathletter2006
You can use the macros \address, \salutation, and \closing for the obvious things. By default, it uses a black-and-white version of the Purdue logo; if you have a color printer and want to use the black-and-gold version, say \goldlogo after you input mathletter.
Tell Brad Lucier if you have problems (but please see plaintest.tex and amstextest.tex first).