Well I found one called vimspell.vim and this is how I implemented it only to auto spell check my e-mail as I type and not any old text document I open up (which got REALLY anoying)
highlight SpellErrors ctermfg=Red cterm=underline term=reverse
set filetype=mail " correct syntax highlighting
set textwidth=72 " wrap at column 72
set editor = "vim -u ~/.mutt/vimrc"
and presto you should have spell checking as you type.
UPDATE - fixed line wrapping issue with long "highlight..." ~/.mutt/vimrc line