To make a formatfile for amstex (to use ams macros with latex you do not
need to create a special format file, just do a \usepackage{amstex} in
the preamble of your LaTeX document), just do the following:

	initex amstex.ini
	mv amstex.fmt /path/to/the/format/files

Now, you can instruct tex to load the format by calling tex (from
your shell) with

	tex \&amstex file.tex

Or, you can create a symbiloc link named amstex that points to virtex:

	ln -s /path/to/virtex amstex
	./amstex file.tex