SSG = SMG = Sequential Manual Gearbox for non-M cars
SMGII = SMG Drivelogic = Sequential ///M Gearbox for M cars
SMG and SMG-D are made by different companies and the electro-hydralic units are very different. Up to now, SMG-D has been 6-speed while SMG has been 5-speed. Both will be 6-speed starting model year 2004. Both have launch control but the SMG-D has a few extra features (e.g. multi-setting for shifting aggressiveness, hill-hold, etc.) The shifting paddles are also different on the two.
Hope this helps.