You cant legally download doom 1 and 2 as far as i know so unless you go on ebay then your outta luck!
doom 2d, not hell on earth its a sidescroller single player version of doom using just the side sprites of classic doom
Oh i must have missed that one before.
If your still looking its here Home of the Underdogs - Entry: DOOM 2D
But good luck getting it to work as it probably needs Dosbox to work properly
Actually, you just need to extract the files out of the ZIP file and then open the DOOM2D.EXE file in the extracted folder. As simple as that.