A word of caution—like all mods, I can’t predict how Aliens TC or my procedure will affect your computer. My process for getting Aliens TC to function has worked of numerous laptops and desktops within my own home, but I don’t know what it’ll do to your machine. Install at your own risk. Anyway, here's how I did it.
Step 1: Install a copy of The Ultimate Doom on your machine. I used the one included on the Doom Collector’s Edition, but I’m pretty sure older versions will work too. The Ultimate Doom wad file is neccessary for running the Doomsday source port.
Step 2: Download Doomsday Engine
(an enhanced Doom source port) here.
This page has all of Doomsday Team’s builds of the engine to date, but the only one that worked for me 100% was 1.9.0-beta4
. I used the Windows version, which is located further down the page in the Windows section. Follow Doomsday’s installation wizard instructions, making sure to select the proper wad file for The Ultimate Doom from your program files directory.
Step 3: Download Aliens Total Conversion Updated
from this website
(scroll down through the list of wads until you find it). It should be version 2.1. You’ll probably have to unzip it. Remember where you save/unzip the folder to, as you’ll need to find it again in the next step.
Sep 4: Open the Doomsday Snowberry launcher from your desktop or program list. Once open, select the addons tab. Click the “+” button to go to the addon installer screen. Click the “…” button to browse your hard drive for the Aliens TC wad folder you downloaded and unzipped in step 3. Once you’ve found the folder, click Open to select it and return to the addons screen. Aliens TC should appear in the list of installable wads. Select Aliens TC, then click install.
Step 5: Once it’s installed, click through the folders on the addons tab until you find the Aliens TC checkbox. Make sure the box is checked. Select The Ultimate Doom from the left hand sidebar.
Click the play button to start the program. If all goes well, you should be playing Aliens TC now, as indicated by the game’s opening screen. Have fun!