The file maxima.vim may be found at:
http://www.vim.org/scripts/script_search_results.php?keywords=maxima&script_type=syntax&order_by=rating&direction=descending&search=search
If possible, this file should be copied to the directory $VIMRUNTIME/syntax.
For Linux Fedora Core 4 this directory is
/usr/share/vim/vim63/syntax
For FreeBSD 5.4 this directory is
/usr/local/share/vim/vim64/syntax
Unfortunately, the "mac" extension is assigned to another type of file, so
I used the extension "mxm" for maxima files. To have vim automatically use
the syntax file maxima.vim for files like "euler.mxm" the file
/usr/share/vim/vim63/filetype.vim
must have the following lines inserted:
" Maxima
au BufNewFile,BufRead *.mxm setf maxima
Since the file maxima.vim is currently not part of the default vim
installation, you must make this change every time you upgrade the
version of vim on your system.
JM Rotenberry