Hi,
juust go to http://www.physicsengine.com/downloads.html
and then you download:
Newton Game Dynamics integration with 3DGS A5/A6. Version 1.5
- Free plug in created by Newton Game Dynamics staff
Needs Game Studio A6 or A5 from Conitec
Includes features and demos from all previous releases. 30 MB

that´s it.
the sdk isn´t the physik plugin.

MfG 3d-master