Yeah man, welcome to DNR. Hope you stick around.
What youre gonna need to do is, go on Ebay, or 3D Realms' website, and buy the Atomic Edition of the game. Its 20 dollars on 3DR's site:
http://3drealms.stores.yahoo.net/games.htmlYou may be able to find it cheaper on Ebay.
When you download Eduke32 (Which you must), it comes with Mapster32, the program you can make levels with, I also recommend the Info Suite that Deeperthough mentioned, and here's a direct link:
http://duke3d.bur.st/index.php?getFile=2505Quite a few people Dukematch, but there are different ways to do it. Most people will recommend using things like Dukkonector and whatnot, but using Hamachi is way easier. Ive only used it for Shadow Warrior, but it likely works the same with Duke. Maybe we can setup a DM match soon.
Also, I dont think anyone has made levels and mods for 1.3 since like 1998. Seriously, get the Atomic Edition, you get a whole new episode!