This is my first up, so I hope everything works like it should :D
I've .rar'd it all quite a few times, so you'll have to unrar it quite a few times, sorry, just wanted to make it as small as possible.
Now, in the Diablo.rar is the Diablo.iso, and the .cue file for it, so you WILL need "Daemon tools", "Alcohol 120%" or something similar. (I suggest www.daemon-tools.cc/)
In the Hellfire.rar is a folder which also includes something called "The Hell" (here for more info www.moddb.com/mods/diablo-the-hell)
You should have no problems running the Hellfire.exe while you've got the Diablo.iso mounted, and so should be able to enjoy :D
Download, seed, and enjoy! :D
P.S. Any issues, lemme know, I'll do my best to help