Hi there, GiRe,
There's no real way to save the whole synth offline and view it as yet. Our fellow Photosynth user, Christoph_Hausner has made a program that downloads the point cloud(s) for any synth and allows you to save them in a number of different 3D model file formats to view in different programs.
You can download his exporter program here: http://synthexport.codeplex.com/
One free program to view the pointclouds in is Meshlab, which you can download here: http://meshlab.sourceforge.net/