Yesterday my roommates bought minecraft too, and we set up a server. What we wanted to know: Is it possible to import a map from a single-player game into the server? I started a huge project some time ago by myself, and we'd like to finish it in multiplayer.
If you use vista or 7 then type %appdata% in the start menu search bar and press enter
if you use xp then go to C:\Documents and Settings \"user name"\Local Settings\Application Data
go into .minecraft then saves then copy the world you want to copy
then start up your server
log on to your server generate the map then close your server and stop it from running
delete the world folder that your server created and paste your world and rename it from world1 or whatever to world
now your world should run on multiplayer