Hi,
The airport bus from Hamburg to Luebeck airport leaves at the central train stationin Hamburg, Airport Bus 20. It costs around 8 Euro (Single).
or you could take the train from Hamburg central station to Luebeck. It takes about 37 minutes (Fast train, ICE) or 45 minutes with the normal train RE (which will be slightly cheaper). There are frequent connections, 2 every hour. www.bahn.de/international/view/en/index.shtml
In Luebeck you then just leave the station, cross the road and walk to the bus station (follow signs for ZOB), take the bus Number 6. It takes about 20 - 25 minutes and drives through the very pretty town centre of Luebeck. I seem to remember it costs less than 2 Euro.
G