This syntax highlighter currently offers only the bare minimum. It needs more work, collaborators welcome.
Put the 4Dg.vim file in ~/.vim/syntax/
Create the syntax folder if it doesn't exist.
From inside vim do :set syntax=4Dg
Add the following line to your vimrc file
autocmd BufNewFile,BufRead *.4Dg,*.4dg set syntax=4Dg
For more information about the vimrc file and where to find it, see
:help vimrc
Create a file called 4dg.vim in $HOME/.vim/ftdetect/ (create the ftdetect folder if it doesn't exist). Add the same line seen in Method 2 to the file. Note that I could not make this work in Windows.