Note that most doomers out there have Doom2 version 1.9. If you have older versions of Doom2, like v1.666 and v1.7a, you are strongly advised to upgrade, using the patch files above. Using Doom2 v1.666 you cannot replay the Mordeth demo's, but you can install the game. To patch up your game to v1.9, please refer to Doomworld's 'patches' section . If one installation prog is choking on your computer configuration, it will tell you this.
Solution is obviously to free more conventional memory by eg.
This means that you cannot use the batch file mordeth.bat to install and run the game. I recently acquired Final Doom, and it appears real easy to make Mordeth compatible with this new version. Here is a description on how to install Mordeth manually for use with Final Doom. Unzip the mordeth.zip archive, leave all files in this subdirectory. Ignore warnings about not being able to find certain files.