The present version is 3.7 (it does not work properly).
Information, such as user guide can be found at http://www.expasy.ch/spdbv/mainpage.htm
The program can be downloaded from: http://www.expasy.ch/spdbv/text/download.htm .
User guide: http://www.expasy.ch/spdbv/text/main.htm
Use Alt-O to open a file (it works even if Open pdb file is not highlighted)
With two structures: open Wind -Layer Infos to control the various layers.
To superimpose two structures (two proteins): Tools - Magic Fit - Ca usually works well.
With File - Save - Save project you can save two superimposed structures.