Should be possible, copy your save game world to the server game world and make sure server.properties ties in your world name.
Basically if this was me doing it and my single player game save was in G:\ftb\ultimate\minecraft\saves\New World I would copy the contents of that folder to my server "world" folder.
So in server.properties there's a line called level-name=world when your server starts up it creates a folder called world and puts an exact (almost) copy of files similar to those in your single player folder.
Steps to get your server going:
Download the server package
Unpack the server download on your server
Run the server to generate all the files
Stop your server
Copy your single player files into the server world folder
Restart your server