you don't have to burn the cd - when you're on the network, connect to the iMac, open iTunes, check "copy when adding" under preferences, then "Add to library..", navigate to the Music > iTunes> iTunes Music folder and choose the mp3s you want to copy across onto your laptop. When you're off the network you won't see the Shared Liibrary, but you'll have local copies of some (or all of it) in your Library.