GET WITH THE PROGRAM
• Install Omen from the forums so you always have the latest updated version.
http://www.minecraftforum.net/viewtopic.php?t=80
• Move the file to a place where you can find it and right click it. Extract it to itself (or just where you have it) so it'll automatically make a new folder.
MAKING IT WORK
• Go to http://minecraft.net/servers.jsp and download 'the server software!'.
• Move the file to wherever Omen is, mainly so you can come back to it easily, and extract it.
• Within your 'minecraft-server' folder, you should see a little Java file called 'minecraft-server.jar'.
**MOVE THIS FOLDER INTO YOUR OMEN FOLDER OR IT WILL NOT SAVE YOUR .DAT FILES***
**AND IT IS NOT THE SAME THING AS 'minecraft.jar'**
• Double-click runOmen.bat within the Omen folder to begin.
GETTING THE MAPS TO MULTIPLAYER
• Go to http://crafted.voziv.com/index.php?module=mcsharp and download the "DatToLvlConverter".
• Move this folder somewhere easy to find (probably best in your Omen folder so you can easily change them without searching) and extract it.
• Within your 'DatConverter' folder, run 'dat to lvl converter.exe'.
• You should see a command (cmd) box come up.
Before you enter your file, know this: The program is picky about spelling and caps. Make it identical to your file. Also add .dat. Example: Foryou.dat
Simply type the name of the file you wish to convert, press Enter a few times then you should have your new map in multiplayer .lvl file form!
Move your new .lvl file to the 'levels' folder of your server folder.
Have fun & good luck!
Also, I'm sorry if there's another tutorial somewhere else but I couldn't find it and I've seen people ask about this 100s of times. I only hope it helps.