NOTE: This guide can be followed if you don't intend to play at school, you just need to make sure that you have the same IWAD and have the game setup on all computers. You can skip the first section if you don't need it.
~~Setting up on the USB Drive~~
Alright so first things first, you must set it up on the USB drive to take it to school(you can use a CD-R/CD-RW, but I used a USB drive). All you need is the Doom IWAD(the IWAD is the necessary part if you don't have it you can use Doom, Doom 2, or FreeDoom. I used Doom 2) Zandronum(or any Source Port really, but I prefer Zandronum), and DoomSeeker. First know the OS the computers you will be running it on use and the download the Archive version, which should only have the core. (Note if the computer at home is different then the ones at school, then you might have to do some setup at school), next download DoomSeeker, again make sure you get the right version for the computers at school.
Now I suggest making a folder in your USB drive, you can call it whatever you want I suggest just calling it Doom. Now Extract the Archives you downloaded(Zandronum and DoomSeeker) into that folder you made. After this there should be two folders inside of the folder that you created(again I named mine Doom 2). Next you can make one or two more folders(I suggest two, for organization), and name one Game Files and one WADs(or just make one named Game Files). Put the IWAD in the Game Files section and put any mods or maps in the WADs folder(or Game Files if you only made one). Now that's it, well that's all you can do at home.
~~Setting it up at school~~
Alright so you are at school, and now what do you do? First off you need to make sure that everyone has it. If they don't go to their computer and copy that Doom Folder you made(I don't suggest putting on the desktop), onto the computer. After that's done make sure that DoomSeeker is setup properly, this is rather easy. First you need to make sure that it's pointing to Zandronum Correctly, and then to the IWAD(Zandronum is located in the Zandronum Folder, and the IWAD in the Game Files folder).Also make sure that if you put the additional Maps, Music, or Mods in a different folder it is pointed to that folder as well. After that add a Custom Server(This is important), make sure the engine is set to Zandronum(or whatever source port you used). Leave this up for the time being(because you need the computers Local IP address, you can get this by doing ipconfig on a windows computer with the Control Prompt open, or using the server). Also make Sure Zandronum also points to the IWAD as well. Have them Launch Zandronum and setup their name for the character they are using also.
~~Setting up the Server~~
Now setting it up on your computer is easy, just plugin your USB Drive(or whatever you used), and setup Zandronum and DoomSeeker just like you did previously, but leave the Custom Server options alone. Next click File in Doom Seeker and click create server, this should open a window. The port should read 1666(although this can be changed), also make sure that both the Engine(Zandronum or the Source Port you used) and the IWAD are loaded. Next make sure that Broadcast to LAN is checked, but Broadcast to Master is not. You can add a server name if you want, but you don't have to. I also suggest setting a few flags(mainly setting up Items and Mega Powerups to respawn) Also if you want to add maps, mods, or music you must add them at this time, click the add button under the General tab(this is the default tab that is open) and add them now, but you must make sure that everyone else has them. After confirming everything is setup properly click start server. Another window should open, KEEP THIS UP, this is where you can manage the server. You can close out the create server window now though. If you want to add bots you can, but you don't have to.
Now if you didn't get the computer's IP Address previously, then look at the bottom of the server window, next to LAN, it should have some Numbers with dots in between, this is the computer's IP address, in the custom servers section make sure everyone has that under the Host Column. Then have them hit okay, your server should pop up in orange, that is the LAN server, have them double click and if everything went fine they should join. Now to join your server just click file then click join server.
And your done.
~~Final Comments~~
That's it. I plan on including video and pictures at a later point, and if you want to help out by making this easier to read, or easier to understand by rewriting portions or taking pictures/video then let me know