I can highly recommend a Baltic cruise, but I think you will find that the earliest cruise to that region will be in May. Both P&O and Cunard sail to the Baltic from Southampton and Fred Olsen and NCL sail from Dover.
P&O and Cunard do Baltic cruises from Southampton. Fred Olsen also but usually from Dover. Cruises for April 2009 onwards have not been published yet. Expect them around April this year.
The scenery in the Baltics is stunning with some fascinating Ports of call but I would not consider going there in the winter,(cold weather, few hours of daylight the further North you go). June onwards is a much nicer time to go, with hopefully better sailing condition.
No cruises to the Baltic in Feb - too flippin chilly.