Come get some
Instructions:
Download the xDuke.zip from the link below.
http://duke3d.org/Database/DFiles_view.php
unzip to your prefered directory.
In the new xduke directory, unzip the Meltdown.zip, and run the setup. When Setup is complete run Meltdown, click on the settings tab, and make sure the directory for "xDuke Exe:" points to duke3d_w32.exe in the "xduke" folder.
If you are behind a router or firewall you will need to open the following ports
UDP 23513 (This can and sometimes needs to be a different port. I would suggest any port, not currently being used by some other application, higher than 23513. You cannot go above 65535. IMPORTANT: If you do decide to use a different port number remember to change it in Meltdown in the settings tab for "Duke Port (UDP):".)
TCP 8501
TCP 8086
Once you are finished you are ready to select a server from the server tab or right click the "Host" column to create your own server. (You may notice a lack of avaliable servers. The Duke Nukem community is almost non-existent. This group was created to attempt to expand that community.)
Information about alternate "netplay guiders" and Duke Nukem ports:
Before you consider alternatives be sure to download the xDuke.zip from the link given above as it contains the DUKE3D.GRP file required by ANY port of the game. Be aware that other Duke Nukem ports are not compatible with each other (i.e. Someone using xDuke cannot play multiplayer with someone who is using eDuke.) Conveniently all netplay guiders listed here support both ports of the game.
Alternatives to Meltdown:
YANG
http://ny.duke4.net/files.html
Dukester X
http://forums.dukesterx.net/dload.php?action=file&file_id=10
Alternatives to xDuke:
eDuke
http://eduke32.com/



