Put the .pk4 file into your C:\Doom 3\base folder.
In order to start the map: 

1) Start Doom 3.
2) Bring down your console (Alt+Ctrl+Tilde) (Tilde is the key next to 1 and under Esc)
3) To play the modern version, type everything behind this arrow -> map The_Focus
4) To play the classic version, type everything behind this arrow -> map The_Focus_Classic

ENJOY!


*** Miscellaneous Information ***

The modern version is a more cinematic and highly immersive, triggered experience.
The classic version plays like the Doom II only the visuals are improved, like the more standard remakes.

The classic version includes 'nostalgic-novelties' such as:
 * Monster infighting.
 * Corresponding difficulty levels. (Including Respawning enemies in Hard difficulty ala Nightmare!)
 * No fall damage.
 * No stamina (You won't get tired by running)
 * The same weapons and monsters in the same locations in the map.
 * Old-skool Keycards.
 * The music track. (In Doomguy's PDA - Making it optional)
 * Only one objective... Find The Exit!

The classic version's difficulty levels:

Easy corresponds to "Hey, Not To Rough."
Medium corresponds to "Ultra-Violence."
Hard corresponds to "Nightmare!"
Nightmare corresponds to 'Ultra Nightmare!!!' (Doom II's Nightmare! Plus Doom 3's Nightmare! = Ultra Nightmare!!!)

WARNING: Hard & Nightmare! modes require a seriously powerful computer.

To make use of them, you may start a new game and choose your diffculty level, wait for the game to finish loading, then bring down your console and start this map typing in -> map The_Focus_Classic

You may also be able to use the console command "g_skill" from 0 to 4 however this is not guaranteed to work.
The benefit to this is that you don't need to start a new game and wait for it to load.

The default difficulty should be Medium, if you do not which to change anything, you shouldn't have to.

* Feedback much appreciated: kevindesmet@yahoo.com

And who knows... if there's enough people who want to see it, I might do a few more.
ENJOY! :)