How to play doom on modern PCs
If you go out and buy the Doom collection, it comes with a front end that will allow you to play on modern systems. But that's no fun!
I found a piece of software called the King Doom Experience (google it) that contains a ton of source ports that gussy doom up with all kinds of graphic effects, extra functionality (you can look up and down now!!), and at long last... true 60FPS 3D!! It's scads of fun, and it'll make you see Doom in a whole new light... it also plays Heretic ^_-. Just download it and use the WAD files from the legal versions of the games.