Most .NFO files use the otherwise uncommon file encoding of cp437. To view them correctly in Vim, the encoding has to be specified.
If you are already viewing the file, just type:
:e ++enc=cp437
That will reload the file forcing the encoding to cp437.
If you want all NFO files to open this way, you can add the following line to your .vimrc
autocmd BufReadPre *.nfo :setlocal fileencodings=cp437,utf-8