Go to this site: Click here[www.osnanet.de].

And click on the link that says the current version of the port.

Once it downloads, cut the archive file and hold the Windows Key on your keyboard, then press the "R" key. In the window that pops up, paste this text:
C:\Program Files (x86)\Steam\SteamApps\common\Final Doom\base

You will be sent to a very important folder. Paste the archive you cut earlier there and extract its contents there using WinRar. I don't know what kind of computer user doesn't use WinRar, so if you don't have it, GRAB IT IMMEDIATELY HERE:Click here to download WinRar[www.win-rar.com]

Unless you prefer 7Zip, of course. Now that everything is extracted, delete "dosbox.exe" and rename "gzdoom.exe" to "dosbox.exe". Now we are ready to do Step 2. You may also want to delete unnecessary files, so it would look like this:
The "dosbox" app in the picture IS GZDoom, it only has automatically changed the icon.
You may also delete the bat files, too.

Open the "gzdoom" PK3 file with WinRar. You'll see a lot of files, but you are only interested in one of them. Open the file named "iwadinfo.txt"(DON'T EXTRACT IT). Now, delete all its contents and paste this:
Now save and close. If the archive asks about updating itself, click "Yes".

Now if you launch Final Doom through Steam, this will pop up:
Yay! Only Final Doom WADs to select! Now you are all set to play with maximum satisfaction possible!






If you know a solution for Zandronum/Skulltag, let me know!