They're probably encoded. The most common encoding methods for mac files online are MacBinary or BinHex. Find some software that can decode those (i think Stuffit for Windows does that) and run the file though it.
Mac files have to be encoded when sent over the internet since it wont preserve the resource or data forks, and macs cant use the file anymore.
It also may have been made on some mac-only program. What on his mac did he initally create the file in?