Screenblast is a cut down "beginners" version of Vegas with limited number of Tracks and restricted functionality.
Acid is a multitrack loop program enabling you to make up pieces of music by mixing and arranging loops together.
Soundforge is a single stereo editor, enabling you to manipulate single tracks of audio, add effects, apply noise rediuction, reverse etc, and/or make looping files ready for use in Acid.
If you have an old SoFo catalog, check out the diffreences between Vegas/Acid vs Videofactory/Acid Music. It's the same diference between Vegas/Acid and the Screenblast products. I don't recomend using the Sony feature lists for the Screenblast products as they are not as complete lists as SoFo put out.