NOTE:
Don't forget to grab a source port which allows you to play DOOM on Windows XP/Vista/7 and many other operating systems! Here's three to get you going:
Chocolate DOOM
A port which emulates the original DOS version of DOOM as closely as possible while keeping functionality on modern computers.
http://www.chocolate-doom.org/wiki/i...Chocolate_Doom
Risen3D
A port that beefs up the DOOM experience with 3D models, HD graphics, remixed sound and music, and more.
http://risen3d.drdteam.org/
Skulltag
A port that allows you to play DOOM online with people around the world.
http://www.skulltag.com/