: Now that I have the mod and Unreal Tournament 1 for playing it, how do I
: install the mod? (It's the Windows version)
My advice... don't. It's not really worth it even though the screenshots look amazing. The Unreal Engine just doesn't fit Marathon's gameplay making some enemies cheap as s'phts on speed, and, no joke, Welcome to the Revolution's exit terminal won't work, so the only way to get to Try Again is by level warping... which strips you of all weapons and ammo you collected. I haven't figured out any cheat to give you all the weapons, but I cheesed through the ending with godmode at that point.
I forgot how you load the assets... I think you legitimately have to replace things in the UT folder. I might check on that tomorrow.