lemme show you how it works: first off, get modloadermp 1.2.5 for servers. then get the gulliver files for the server. put them all in the minecraft_server.jar. but do NOT delete meta-inf, that's only for clients! hope this helped.
just what you said. take a screenshot (F2) of your build in minecraft, and then in the upload menu, choose Images & Video. then, click add file and select browse. then, search for your picture in your minecraft screenshots folder (name it beforehand or put it to desktop to make it easier to find) then add a caption and select upload file! (of course, don't forget to upload the zip to an file-sharing site, copy that url and paste it in World Download URL in project details.)