After posting my VIM MSH syntax file on the internal Monad discussion list, I got a great reply from Tommy Williams who obviously knows more about how to tweak VIM than I do. Tommy showed me the right way to add a custom syntax file to your VIM setup without potentially screwing up your upgradability. He also added support for comments, which in itself is worth the update. Thanks Tommy!
Here is the new msh.vim file. If you followed my previous instructions, then begin by undoing all of it.  _place_holder;Then download this new msh.vim file and follow Tommy’s instructions:
The best explanation I can find for it in the help files is with :help runtimepath. That shows you the directories and files.
In this case, there are two directories and three files involved:
Msh.vim is the file you supplied as monad.vim.
For me, this is just a series of blocks of the form:
au BufNewFile,BufRead *.<extension> _place_holder; _place_holder; _place_holder; _place_holder; setf <extension>
In the case of MSH:
au BufNewFile,BufRead, *.msh _place_holder; _place_holder; _place_holder; setf msh
This is a file where I set things like indenting, textwidth, etc. for that filetype: things you can’t - or shouldn’t - do in a syntax file. So far it’s just a shell. I’ll tweak it to add more options later, but it should give you a feel for things:
" Only do this when not done yet for this buffer
if exists("b:did_ftplugin") | finish | endif
" Don't load another plug-in for this buffer
let b:did_ftplugin = 1
" Change the browse dialog on Win32 to show mainly MSH-related files
let b:browsefilter = "MSH Files (*.msh)\t*.msh\n" .
\ "All Files (*.*)\t*.*\n"
" Undo the stuff we changed.
let b:undo_ftplugin = "setlocal tw< cms< fo<" .
\ " | unlet! b:browsefilter"
" vim: ts=4:tw=0
And, of course, the syntax\msh.vim file is the one you made.
Now playing: AC/DC - Rocker
UPDATE 2005-08-12: Posted it to the vim.org scripts section.
UPDATE 2005-08-13: I made a small change to the syntax file that fixed a problem with foreach and while. The current version is 1.2. I will also be re-posting it to the vim.org scripts board.