"Synching" with new computer and maintaining playlists

I bought a new iMac in July, but continued to synch my iPhone4 with my older MacBook. I would like to switch over to synching with the iMac, but don't want to lose my playlists, music files, etc, which are currently stored on the iPhone. Is there a way to pull the playlists off the phone into the iMac? (All of my music files are on an external 2TB drive that synchs that is available to all macs in the house via my airport network. The other issue, which is slightly related, is that the MacBook's iTunes library recently changed itself and forgot where it's library was. In choosing the correct library, a lot of my playlists were gone and some of the music was also gone. The MacBook has 3 hard drives (one internal; 2 external that are always on), 2 of which are bootable. Booting from a different drive still doesn't pull up the iTunes library as it occurred a month ago. I tried pulling it out of Time Machine, but it didn't work. So, synching with the MacBook is also impossible, since again, my iPhone playlists will be erased. So, how can I pull the music & playlists off of the iPhone before synching with the new computer? (I should reiterate that I am not in danger of losing the music, since it's all on the external music-server drive, but the playlists will all disappear.)