01kipper: No luck unfortunately :(, thanks for the suggestion though! I think it may be a problem with the version of ZDoom I'm using, it doesn't recognise the new wad for whatever reason (I'm not very experienced with using source ports)
amrit9037: Does Mac supports Drag and Drop? You can try that.
If you want to play through the game and get to Romero's level naturally, select "New Game," and then the "Knee Deep in the Dead" episode from the next menu. You'll have to get through the first seven, original Doom levels before you reach Romero's new creation.
Alternatively, you can cheat. Start up a new game as normal and, once you have control of your character, type the following: idclev18. (Not the period.) That will instantly warp you to level eight. If you cheat your way there, you might also want to type in "idfa" (not the quotes) to give yourself a bunch of weapons. And if you really want to cheat, type "iddqd" to activate "god mode" and render yourself invulnerable to damage.
Drag-and-drop doesn't seem to work, I still get the original e1m8. I've been using the idclev18 cheat you mentioned to jump there quickly (and idkfa for the guns) :).