Here it is: the original Halo game for PC. All you have to do is:

1. Burn the ISO to a disk or mount it with any disk mounting app (I suggest Daemon Tools)
   
2. Install it (the serial is in the "patch" folder on the CD)
3. Replace the "halo.exe" file in the installation path the the file in the "patch" folder named halo 1 No-CD Patch. It's a .rar file, so you'll need WinRAR or Alzip to open it.
4. Play!

Here is the folder:
http://www.mediafire.com/?sharekey=06f69c76789e08b87069484bded33bcdd19a12212d7b2cdc